Transmission device, transmission method, and communication system

ABSTRACT

A transmission device of the present disclosure includes: a driver unit that transmits a data signal with use of a first voltage state, a second voltage state, and a third voltage state interposed between the first voltage state and the second voltage state, and is configured to make a voltage in the third voltage state changeable; and a controller that changes the voltage in the third voltage state to cause the driver unit to perform emphasis.

TECHNICAL FIELD

The present disclosure relates to a transmission device that transmits asignal, a transmission method used in such a transmission device, and acommunication system including such a transmission device.

BACKGROUND ART

In association with high functionality and multi-functionality ofelectronic apparatuses in recent years, the electronic apparatusesinclude various devices such as a semiconductor chip, a sensor, and adisplay device. A lot of pieces of data are exchanged between thesedevices, and the amount of such data has been increased with highfunctionality and multi-functionality of the electronic apparatuses.Accordingly, the data are frequently exchanged with use of a high-speedinterface that allows for transmission and reception of data at severalGbps, for example.

In order to improve communication performance in the high-speedinterface, various technologies have been disclosed. For example, PTLs 1and 2 each disclose a communication system that transmits threedifferential signals with use of three transmission paths. Moreover, forexample, PLT 3 discloses a communication system that performspre-emphasis.

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication No. H06-261092

PTL 2: U.S. Pat. No. 8,064,535

PTL 3: Japanese Unexamined Patent Application Publication No.2011-142382

As described above, in the communication system, an improvement incommunication performance is desired, and a further improvement incommunication performance is expected.

It is desirable to provide a transmission device, a transmission method,and a communication system that allow for enhancement of communicationperformance.

SUMMARY OF THE INVENTION

A transmission device according to an embodiment of the presentdisclosure includes a driver unit and a controller. The driver unittransmits a data signal with use of a first voltage state, a secondvoltage state, and a third voltage state interposed between the firstvoltage state and the second voltage state, and is configured to make avoltage in the third voltage state changeable. The controller changesthe voltage in the third voltage state to cause the driver unit toperform emphasis.

A transmission method according to an embodiment of the presentdisclosure includes: transmitting a data signal with use of a firstvoltage state, a second voltage state, and a third voltage stateinterposed between the first voltage state and the second voltage state,and changing a voltage in the third voltage state to perform emphasis.

A communication system according to an embodiment of the presentdisclosure includes a transmission device and a reception device. Thetransmission device includes a driver unit and a controller. The driverunit transmits a data signal with use of a first voltage state, a secondvoltage state, and a third voltage state interposed between the firstvoltage state and the second voltage state, and is configured to make avoltage in the third voltage state changeable. The controller changesthe voltage in the third voltage state to cause the driver unit toperform emphasis.

In the transmission device, the transmission method, and thecommunication system according to the embodiments of the presentdisclosure, the data signal is transmitted with use of the first voltagestate, the second voltage state, and the third voltage state. Thevoltage in the third voltage state is changeable. Further, the voltagein the third voltage state is changed to perform emphasis.

According to the transmission device, the transmission method, and thecommunication system of the embodiments of the present disclosure, thevoltage in the third voltage state interposed between the first voltagestate and the second voltage state is changed to perform emphasis, whichmakes it possible to enhance communication performance. It is to benoted that effects described here are not necessarily limited and mayinclude any of effects described in the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a configuration example of acommunication system according to an embodiment of the presentdisclosure.

FIG. 2 is an explanatory diagram illustrating voltage states of signalsto be transmitted and received by the communication system illustratedin FIG. 1.

FIG. 3 is an explanatory diagram illustrating transition of a symbol tobe transmitted and received by the communication system illustrated inFIG. 1.

FIG. 4 is a block diagram illustrating a configuration example of atransmitter illustrated in FIG. 1.

FIG. 5 is a table illustrating an operation example of a transitiondetector illustrated in FIG, 4.

FIG. 6 is a table illustrating an operation example of an output unitillustrated in FIG. 4.

FIG. 7 is a block diagram illustrating a configuration example of anoutput unit according to a first embodiment.

FIG. 8 is a timing waveform diagram illustrating an operation example ofa timing controller illustrated in FIG. 7.

FIG. 9 is a block diagram illustrating a configuration example of areceiver illustrated in FIG. 1.

FIG. 10 is an explanatory diagram illustrating an example of a receptionoperation of the receiver illustrated in FIG. 9.

FIG. 11 is another explanatory diagram illustrating an example of areception operation of the receiver illustrated in FIG. 9.

FIG. 12 is an eye diagram schematically illustrating a characteristicexample of the communication system.

FIG. 13A is a timing waveform diagram illustrating an operation exampleof a communication system according to the first embodiment.

FIG. 13B is another timing waveform diagram illustrating an operationexample of the communication system according to the first embodiment,

FIG. 13C is another timing waveform diagram illustrating an operationexample of the communication system according to the first embodiment.

FIG. 13D is another timing waveform diagram illustrating an operationexample of the communication system according to the first embodiment.

FIG. 13E is another timing waveform diagram illustrating an operationexample of the communication system according to the first embodiment.

FIG. 14A is an eye diagram illustrating a characteristic example of thecommunication system according to the first embodiment.

FIG. 14B is another eye diagram illustrating a characteristic example ofthe communication system according to the first embodiment.

FIG. 14C is another eye diagram illustrating a characteristic example ofthe communication system according to the first embodiment.

FIG. 14D is another eye diagram illustrating a characteristic example ofthe communication system according to the first embodiment.

FIG. 15A is a timing waveform diagram illustrating an operation exampleof a communication system according to a comparative example.

FIG. 15B is another timing waveform diagram illustrating an operationexample of the communication system according to the comparativeexample.

FIG. 15C is another timing waveform diagram illustrating an operationexample of the communication system according to the comparativeexample.

FIG. 15D is another timing waveform diagram illustrating an operationexample of the communication system according to the comparativeexample.

FIG. 15E is another timing waveform diagram illustrating an operationexample of the communication system according to the comparativeexample.

FIG. 16 is a block diagram illustrating a configuration example of anoutput unit according to a modification example of the first embodiment.

FIG. 17 is a circuit diagram illustrating a configuration example of adriver unit illustrated in FIG. 16.

FIG. 18 is a block diagram illustrating a configuration example of anoutput unit according to a second embodiment,

FIG. 19 is a circuit diagram illustrating a configuration example of adriver unit illustrated in FIG. 18.

FIG. 20 is a table illustrating an operation example of the output unitillustrated in FIG. 18.

FIG. 21A is a schematic view of an operation example of the output unitillustrated in FIG. 18.

FIG. 21B is another schematic view of an operation example of the outputunit illustrated in FIG. 18.

FIG. 21C is another schematic view of an operation example of the outputunit illustrated in FIG. 18.

FIG. 22A is a timing waveform diagram illustrating an operation exampleof a communication system according to the second embodiment.

FIG. 22B is another timing waveform diagram illustrating an operationexample of the communication system according to the second embodiment.

FIG. 22C is another timing waveform diagram illustrating an operationexample of the communication system according to the second embodiment.

FIG. 22D is another timing waveform diagram illustrating an operationexample of the communication system according to the second embodiment.

FIG. 22E is another timing waveform diagram illustrating an operationexample of the communication system according to the second embodiment.

FIG. 23 is an eve diagram illustrating a characteristic example of thecommunication system according to the second embodiment.

FIG. 24 is a perspective view of an external appearance configuration ofa smartphone to which the communication system according to theembodiment is applied.

FIG. 25 is a block diagram illustrating a configuration example of anapplication processor to which the communication system according to theembodiment is applied.

FIG. 26 is a block diagram illustrating a configuration example of animage sensor to which the communication system according to theembodiment is applied.

FIG. 27 is a block diagram illustrating a configuration example of avehicle control system to which the communication system according tothe embodiment is applied.

MODES FOR CARRYING OUT THE INVENTION

In the following, some embodiments of the present disclosure aredescribed in detail with reference to the drawings. It is to be notedthat description is given in the following order.

1. First Embodiment

2. Second Embodiment

3. Application Examples

<1. First Embodiment>

[Configuration Example]

FIG. 1 illustrates a configuration example of a communication system (acommunication system 1) according to a first embodiment. Thecommunication system 1 improves communication performance bypre-emphasis.

The communication system 1 includes a transmission device 10, atransmission path 100, and a reception device 30. The transmissiondevice 10 includes three output terminals ToutA, ToutB, and ToutC. Thetransmission path 100 includes three lines 110A, 110B, and 110C. Thereception device 30 includes three input terminals TinA, TinB, and TinC.Further, the output terminal ToutA of the transmission device 10 and aninput terminal TinA of the reception device 30 are coupled to each otherthrough the line 110A. The output terminal ToutB of the transmissiondevice 10 and the input terminal TinB of the reception device 30 arecoupled to each other through the line 110B. The output terminal ToutCof the transmission device 10 and the input terminal TinC of thereception device 30 are coupled to each other through the line 110C.Characteristics impedances of the lines 110A to 110C are about 50 [Ω] inthis example.

The transmission device 10 respectively outputs a signal SIGA, a signalSIGB, a signal SIGC from the output terminal ToutA, the output terminalToutB, and the output terminal ToutC. Thereafter, the reception device30 respectively receives the signal SIGA, the signal SIGB, and thesignal SIGC through the input terminal TinA, the input terminal TinB,and the input terminal TinC. The signals SIGA, SIGB, and SIGC eachpossibly take three voltage states SH, SM, and SL. Herein, the voltagestate SM is a state corresponding to a medium-level voltage VM. In otherwords, a voltage indicated by the voltage state SM includes, in additionto the medium-level voltage VM, a voltage in a case where pre-emphasisis performed on the medium-level voltage VM, as will be described later.Likewise, the voltage state SH is a state corresponding to a high-levelvoltage VH, and the voltage state SL is a state corresponding to alow-level voltage VL.

FIG. 2 illustrates voltage states of the signals SIG-A, SIGB, and SIGC.The transmission device 10 uses the three signals SIGA, SIGB, and SIGCto transmit six symbols “+x”, “+y”, “−y”, “+z”, and “−z”. For example,in a case where the transmission device 10 transmits the symbol “+x”,the transmission device 10 respectively sets the signal SIGA, the signalSIGB, and the signal SIGC to the voltage state SH (for example, thehigh-level voltage VH), the voltage state SL (for example, the low-levelvoltage VL), and the voltage state SM (for example, the medium-levelvoltage VM). In a case where the transmission device 10 transmits thesymbol “−x”, the transmission device 10 respectively sets the signalSIGA, the signal SIGB, and the signal SIGC to the voltage state SL, thevoltage state SH, and the voltage state SM. In a case where thetransmission device 10 transmits the symbol “+y”, the transmissiondevice 10 respectively sets the signal SIGA, the signal SIGB, and thesignal SIGC to the voltage state SM, the voltage state SH, and thevoltage state SL. In a case where the transmission device 10 transmitsthe symbol “−y”, the transmission device 10 respectively sets the signalSIGA, the signal SIGB, and the signal SIGC to the voltage state SM, thevoltage state SL, and the voltage state SH. In a case where thetransmission device 10 transmits the symbol “+z”, the transmissiondevice 10 respectively sets the signal SIGA, the signal SIGB, and thesignal SIGC to the voltage state SL, the voltage state SM, and thevoltage state SH. In a case where the transmission device 10 transmitsthe symbol “−z”, the transmission device 10 respectively sets the signalSIGA, the signal SIGB, and the signal SIGC to the voltage state SH, thevoltage state SM, and the voltage state SL.

The transmission path 100 transmits a sequence of symbols with use ofsuch signals SIGA, SIGB, and SIGC. In other words, three lines 110A,110B, and 110C serves as one lane that transmits the sequence ofsymbols.

(Transmission Device 10)

The transmission device 10 includes a clock generator 11, a processor12, and a transmitter 20, as illustrated in FIG. 1.

The clock generator 11 generates a clock signal TxCK. A frequency of theclock signal TxCK is, for example, 2.5 [GHz]. It is to be noted that thefrequency is not limited thereto, and, for example, in a case where acircuit in the transmission device 10 is configured with use of aso-called half-rate architecture, it is possible to set the frequency ofthe clock signal TxCK to 1.25 [GHz]. The clock generator 11 isconfigured with use of, for example, a PLL (Phase Locked Loop), andgenerates the clock signal TxCK on the basis of, for example, areference clock (not illustrated) supplied from outside of thetransmission device 10. Thereafter, the clock generator 11 supplies theclock signal TxCK to the processor 12 and the transmitter 20.

The processor 12 performs predetermined processing to generatetransition signals TxF0 to TxF6, TxR0 to TxR6, and TxP0 to TxP6. Herein,a group of the transmission signals TxF0, TxR0, and TxP0 indicates asymbol transition in a sequence of symbols that is to be transmitted bythe transmission device 10. Likewise, a group of the transition signalsTxF1, TxR1, and TxP1 indicates a symbol transition, a group of thetransition signals TxF2, TxR2, and TxP2 indicates a symbol transition, agroup of the transition signals TxF3, TxR3, and TxP3 indicates a symboltransition, a group of the transition signals TxF4, TxR4, and TxP4indicates a symbol transition, a group of the transition signals TxF5,TxR5, and TxP5 indicates a symbol transition, and a group of thetransition signals TxF6, TxR6, and TxP6 indicates a symbol transition.In other words, the processor 12 generates seven groups of transitionsignals. Hereinafter, on an as-needed basis, transition signals TxF,TxR, and TxP are used as indication of any of the seven groups oftransition signals.

FIG. 3 illustrates a relationship between the transition signals TxF,TxR, and TxP and symbol transitions. Numerical values of three digitsgiven to each transition indicate values of the transition signals TxF,TxR, and TxP in this order.

The transition signal TxF (Flip) causes a symbol transition between “+x”and “−x”, a symbol transition between “+y” and “−y”, and a symboltransition between “+z” and “−z”. Specifically, in a case where thetransition signal TxF is “1”, a transition is made to change thepolarity of the symbol (for example, from “+x” to “−x”), and in a casewhere the transition signal TxF is “0”, such a transition is not made.

The transition signals TxR (Rotation) and TxP (Polarity) cause symboltransitions between “+x” and a symbol other than between “+y” and asymbol other than “−y”, and between “+z” and a symbol other than “−z”.Specifically, in a. case where the transition signals TxR and TxP arerespectively “1” and “0”, a transition is made in a clockwise directionin FIG. 3 while keeping the polarity of the symbol (for example, from“±x” to “+y”), and in a case Where the signals TxR and TxP arerespectively “1” and “1”, a transition is made in the clockwisedirection in FIG. 3 while changing the polarity of the symbol (forexample, from “+x” to “−y”). Moreover, in a case where the transitionsignals TxR and TxP are respectively “0” and “0”, a transition is madein a counterclockwise direction in FIG. 3 While keeping the polarity ofthe symbol (for example, from “+x” to “+z”), and in a case where thetransition signals TxR and TxP are respectively “0” and “1”, atransition is made in the counterclockwise direction in FIG. 3 whilechanging the polarity of the symbol (for example, from “+x” to “−z”).

The processor 12 generates such seven groups of the transition signalsTxF, TxR. and TxP. Thereafter, the processor 12 supplies the sevengroups of the transition signals TxF, TxR, and TxP (the transitionsignals TxF0 to TxF6, TxR0 to TxR6, and TxP0 to TxP6) to the transmitter20.

The transmitter 20 generates the signals SIGA, SIGB, and SIGC on thebasis of the transition signals TxF0 to TxF6, TxR0 to TxR6, and TxP0 toTxP6.

FIG. 4 illustrates a configuration example of the transmitter 20. Thetransmitter 20 includes serializers 21F, 21R, and 21P, a transmissionsymbol generator 22, a transition detector 25, and an output unit 26.

The serializer 21F serializes the transition signals TxF0 to TxF6 inthis order on the basis of the transition signals TxF0 to TxF6 and theclock signal TxCK to generate a transition signal TxF9. The serializer21R serializes the transition signals TxR0 to TxR6 in this order on thebasis of the transition signals TxR0 to TxR6 and the clock signal TxCKto generate a transition signal TxR9. The serializer 21P serializes thetransition signals TxP0 to TxP6 in this order on the basis of thetransition signals TxP0 to TxP6 and the clock signal TxCK to generate atransition signal TxP9.

The transmission symbol generator 22 generates symbol signals Tx1, Tx2,and Tx3 on the basis of the transition signals TxF9, TxR9. and TxP9 andthe clock signal TxCK. The transmission symbol generator 22 includes asignal generator 23 and a flip-flop 24.

The signal generator 23 generates the symbol signal Tx1, Tx2, and Tx3 onthe basis of the transition signals TxF9, TxR9, and TxP9 and symbolsignals D1, D2, and D3. Specifically, the signal generator 23 determinesa symbol NS after the transition as illustrated in FIG. 3 on the basisof a symbol indicated by the symbol signals D1, D2, and D3 (a symbol DSbefore the transition) and the transition signals TxF9, TxR9, and TxP9,and outputs the symbol NS as the symbol signals Tx1, Tx2, and Tx3.

The flip-flop 24 samples the symbol signals Tx1, Tx2, and Tx3 on thebasis of the clock signal TxCK and respectively outputs sampling resultsof the symbol signals Tx1, Tx2, and Tx3 as the symbol signals D1, D2,and D3.

FIG. 5 illustrates an operation example of the transmission symbolgenerator 22. FIG. 5 illustrates the symbol NS generated on the basis ofthe symbol DS indicated by the symbol signals D1, D2, and D3 and thetransition signals TxF9, TxR9, and TxP9. Description is given withreference to an example in which the symbol DS is “+x”. In a case wherethe transition signals TxF9, TxR9, and TxP9 are “000”, the symbol NS is“+z”, in a case where the transition signals TxF9, TxR9, and TxP9 are“001” the symbol NS is “−z”, in a case where the transition signalsTxF9, TxR9, and TxP9 are “010”, the symbol NS is “−z”, in a case wherethe transition signals TxF9, TxR9, and TxP9 are “011”, the symbol NS is“−y”, and in a case where the transition signals TxF9, TxR9, and TxP9 is“1xx”, the symbol NS is “−x”. Herein, “x” indicates that a signal may heeither “1” or “0”. This also applies to a case where the symbol DS is“−x”, a case where the symbol DS is “+y”, a case where the symbol DS is“−y”, a case where the symbol DS is “+z”, and a case where the symbol DSis “−z”.

The transition detector 25 generates pre-emphasis control signals MUPand NIDN on the basis of the transition signals TxF9, TxR9, and TxP9 andthe symbol signals D1, D2, and D3. Specifically, in a case where thetransition signals TxF9, TxR9, and TxP9 are “000” and the symbol DSindicated by the symbol signals D1, D2, and D3 are “+x”, “+y”, and “+z”,and in a case where the transition signals TxF9, TxR9, and TxP9 are“010” and the symbol DS indicated by the symbol signals D1, D2, and D3are “−x”, “−y”, and “−z”, the transition detector 25 respectively setsthe pre-emphasis control signal MUP and the pre-emphasis control signalMDN to “1” (active) and “0” (inactive), as indicated by WUP circled by asolid line in FIG. 5. Moreover, in a case where the transition signalsTxF9, TxR9, and TxP9 are “000” and the symbol DS indicated by the symbolsignals D1, D2, and D3 is “−x”, “−y”, and “−z”, and in a case where thetransition signals TxF9, TxR9. and TxP9 are “010” and the symbol DSindicated by the symbol signals D1, D2, and D3 is “+z”, “+v”, and “+z”,the transition detector 25 respectively sets the pre-emphasis controlsignal MDN and the pre-emphasis control signal MUP to “1” (active) and“0” (inactive) as indicated by WDN circled by a broken line in FIG. 5.Further, transition detector 25 sets both the pre-emphasis controlsignals MUP and MDN to “0” (inactive) in other cases. In other words, aswill be described later, in a case where the transition signals TxF9,TxR9, and TxP9 are “000” or “010”, there is a possibility that atransition time of any of a difference AB between the signal SIGA andthe signal SIGB, a difference BC between the signal SIGB and the signalSIGC, and a difference CA between the signal SIGC and the signal SIGAbecomes long. Accordingly, the transition detector 25 confirms, on thebasis of the transition signals TxF9, TxR9, and TxP9 and the symbolsignals D1, D2, and D3, whether or not the symbol transition is a symboltransition having the possibility that the transition time of any of thedifferences AB, BC, and CA becomes long, and generates the pre-emphasiscontrol signals MUP and MDN on the basis of a thus-obtained result.

The output unit 26 generates the signals SIGA, SIGB, and SIGC on thebasis of the symbol signals Tx1, Tx2, and Tx3 and the clock signal TxCK.

FIG. 6 illustrates an operation example of the output unit 26. Forexample, in a case where the symbol signal Tx1, Tx2, and Tx3 are “100”,the output unit 26 respectively sets the signal SIGA, the signal SIGB,and the signal SIGC to the voltage state SH (for example, the high-levelvoltage VH), the voltage state SL (for example, the low-level voltageVL), and the voltage state SM (for example, the medium-level voltageVM). In other words, the output unit 26 generates the symbol “+x”.Moreover, for example, in a case where the symbol signals Tx1, Tx2, andTx3 are “011”, the signal SIGA, the signal SIGB, and the signal SIGC arerespectively set to the voltage state SL, the voltage state SH, and thevoltage state SM. In other words, the output unit 26 generates thesymbol “−x”. Further, for example, in a case where the symbol signalsTx1, Tx2, and Tx3 are “010”, the signal SIGA, the signal SIGB, and thesignal SIGC are respectively set to the voltage state SM, the voltagestate SH, and the voltage state SL. In other words, the output unit 26generates the symbol “−y”. Furthermore, for example, in a case where thesymbol signals Tx1, Tx2, and Tx3 are “101”, the signal SIGA, the signalSIGB, and the signal SIGC are respectively set to the voltage state SM,the voltage state SL, and the voltage state SH. In other words, theoutput unit 26 generates the symbol “−y”. Moreover, for example, in acase where the symbol signals Tx1, Tx2, and Tx3 are “001”, the signalSIGA, the signal SIGB, and the signal SIGC are respectively set to thevoltage state SL, the voltage state SM, and the voltage state SH. Inother words, the output unit 26 generates the symbol “+z”. Further, forexample, in a case where the symbol signals Tx1, Tx2, and Tx3 are “110”,the signal SIGA, the signal SIGB, and the signal SIGC are respectivelyset to the voltage state SH, the voltage state SM, and the voltage stateSL. In other words, the output unit 26 generates the symbol “−z”.

FIG. 7 illustrates a configuration example of the output unit 26. Theoutput unit 26 includes a driver controller 27, a timing controller 27T,pre-emphasis controllers 28A, 28B, and 28C, and driver units 29A, 29B,and 29C.

The driver controller 27 generates signals PUA, PDA, PUB, PDB, PUC, andPDC on the basis of the symbol signals Tx1, Tx2, and Tx3 and the clocksignal TxCK. Specifically, as illustrated in FIG. 6, for example, in acase where the signal SIGA is set to the voltage state SH (for example,the high-level voltage VH), the driver controller 27 respectively setsthe signal PUA and the signal PDA to “1” and “0”, and in a case wherethe signal SIGA is set to the voltage state SL (for example, thelow-level voltage VL), the driver controller 27 respectively sets thesignal PDA and the signal PUA to “1” and “0”, and in a case where thesignal SIGA is set to the voltage state SM (for example, themedium-level voltage VM), the driver controller 27 sets both the signalsPUA and PDA to “1”. This also applies to the signals PUB and PDB and thesignals PUC and PDC. Thereafter, the driver controller 27 supplies thesignals PUA and PDA to the pre-emphasis controller 28A, supplies thesignals PUB and PDB to the pre-emphasis controller 28B, and supplies thesignals PVC and PDC to the pre-emphasis controller 28C.

On the basis of the pre-emphasis control signals MUP and MDN and theclock signal TxCK, the timing controller 27T performs timing adjustmenton the pre-emphasis control signal MUP to generate a pre-emphasiscontrol signal MUP2, and performs timing adjustment on the pre-emphasiscontrol signal MDN to generate a pre-emphasis control signal MDN2.Thereafter, the timing controller 27T supplies the pre-emphasis controlsignals MUP2 and MDN2 to the pre-emphasis controllers 28A to 28C.

FIG. 8 illustrates an example of waveforms of the signals PUA and PDAand pre-emphasis control signals MUP2 and MDN2 that are to be suppliedto the pre-emphasis controller 28A. The signals PUA and PDA may changein every time period (unit interval UI) corresponding to one symbol. Inthis example, the signal PUA changes from a low level to a high level ata timing t1, changes from the high level to the low level at a timing t3after a lapse of a time period corresponding to two unit intervals UIfrom the timing t1, changes from the low level to the high level at atiming t4 after a lapse of a time period corresponding to one unitinterval UI from the timing t3, and changes from the high level to thelow level at a timing t5 after a lapse of a time period corresponding toone unit interval UI from the timing t4 (FIG. 8(A)). Moreover, thesignal PDA changes from the high level to the low level at a timing t2after a lapse of a time period corresponding to one unit interval UIfrom the timing t1, and changes from the low level to the high level atthe timing t3 (FIG. 8(B)). Moreover, the pre-emphasis control signalsMUP2 and MDN2 are changeable from the low level to the high level at astart timing of the unit interval UI, and are changeable from the highlevel to the low level at a timing after a lapse of a time periodcorresponding to a half (0.5 UI) of the unit interval UI from the starttiming of the unit interval UI. In this example, the pre-emphasiscontrol signal MUP2 changes from the low level to the high level at thetiming t1, and changes from the high level to the low level at a timingafter a lapse of a time period corresponding to a half (0.5 UI) of theunit interval UI from the timing t1 (FIG. 8(C)). Further, thepre-emphasis control signal MDN2 changes from the low level to the highlevel at the timing t4, and changes from the high level to the low levelat a timing after a lapse of a time period corresponding to a half (0.5UI) of the unit interval UI from the timing t4 (FIG. 8(D)). In thisexample, signals to be supplied to the pre-emphasis controller 28A aredescribed; however, this also applies to signals to be supplied to thepre-emphasis controllers 28B and 28C. As described above, the timingcontroller 27T performs timing adjustment on the pre-emphasis controlsignals MUP and MDN to change the pre-emphasis control signals MUP2 andMDN2 from the low level to the high level at the start timing of theunit interval UI and change the pre-emphasis control signals MUP2 andMDN2 from the high level to the low level at a timing after a lapse of atime period corresponding to a half (0.5 UI) of the unit interval UIfrom that timing.

The pre-emphasis controller 28A generates signals PUA1 to PUA24 and PDA1to PDA24 on the basis of the signals PUA and PDA and the pre-emphasiscontrol signals MUP2 and MDN2. The driver unit 29A generates the signalSIGA on the basis of the signals PUA1 to PUA24 and PDA1 to PDA24. Thedriver unit 29A includes twenty four drivers 29A1 to 29A24 in thisexample. The driver 29A1 operates on the basis of the signals PUA1 andPDA1, and the driver 29A2 operates on the basis of the signals PUA2 andPDA2. This also applies to the drivers 29A3 to 29A23. The driver 29A24operates on the basis of the signals PUA24 and PDA24. Output terminalsof the drivers 29A1 to 29A24 are coupled to one another, and are coupledto the output terminal ToutA. It is to be noted that in this example,twenty four drivers 29A1 to 29A24 are provided; however, the number ofdrivers are not limited thereto. Alternatively, twenty three or less ortwenty five or more drivers may be provided.

The pre-emphasis controller 28B generates signals PUB1 to PUB24 and PDB1to PDB24 on the basis of the signals PUB and PDB and the pre-emphasiscontrol signals MUP2 and MDN2, as with the pre-emphasis controller 28A.The driver unit 29B generates the signal SIGB on the basis of thesignals PUB1 to PUB24 and PDB1 to PDB24, as with the driver unit 29A.The driver unit 29B includes twenty four drivers 29B1 to 29B24 in thisexample. Output terminals of the drivers 29B1 to 29B24 are coupled toone another, and are coupled to the output terminal ToutB.

The pre-emphasis controller 28C generates signals PUC1 to PUC24 and PDC1to PDC24 on the basis of the signal PUC and PDC and the pre-emphasiscontrol signals MUP2 and MDN2, as with the pre-emphasis controller 28A.The driver unit 29C generates the signal SIGC on the basis of thesignals PUC1 to PUC24 and PDC1 to PDC24, as with the driver unit 29A.The driver unit 29C includes twenty four drivers 29C1 to 29C24 in thisexample. Output terminals of the drivers 29C1 to 29C24 are coupled toone another, and are coupled to the output terminal ToutC.

Next, configurations of the drivers 29A1 to 29A24, 29B1 to 29B24, and29C1 to 29C24 are described with reference to the driver 29A1 as anexample. The driver 29A1 includes transistors 91 and 94 and resistors 92and 93. The transistors 91 and 94 in this example each are an N-channelMOS (Metal Oxide Semiconductor)-FET (Field Effect Transistor). A gate ofthe transistor 91 is supplied with the signal PUA1, a drain thereof issupplied with a voltage V1, and a source thereof is coupled to one endof the resistor 92. A gate of the transistor 94 is supplied with thesignal PDA1, a drain thereof is coupled to one end of the resistor 93,and a source thereof is grounded. The one end of the resistor 92 iscoupled to the source of the transistor 91, and the other end thereof iscoupled to the other end of the resistor 93 and the output terminalToutA of the transmission device 10. The one end of the resistor 93 iscoupled to the drain of the transistor 94, and the other end thereof iscoupled to the other end of the resistor 92 and the output terminalToutA of the transmission device 10. In this example, the sum of aresistance value of on resistance of the transistor 91 and a resistancevalue of the resistor 92 is about 1000[Ω]. Likewise, the sum of aresistance value of on resistance of the transistor 94 and a resistancevalue of the resistor 93 is about 1000[Ω].

With this configuration, for example, the driver controller 27 sets avoltage state at the output terminal ToutA to one of the three voltagestates SH, SM, and SL with use of the signals PUA and PDA. Specifically,for example, in a case where the voltage of the signal SIGA is set tothe high-level voltage VH (the voltage state SH), the driver controller27 respectively sets the signal PUA and the signal PDA to “1” and “0”.This causes the pre-emphasis controller 28A to set twenty of the signalsPUA1 to PUA24 to “1”, and to set the remaining four of the signals PUA1to PUA24 and the signals PDA1 to PDA24 to “0”. At this time, in thedriver unit 29A, twenty of the twenty four transistors 91 are turned on.As a result, the signal SIGA is set to the high-level voltage VH, and anoutput termination resistance (output impedance) of the driver unit 29Abecomes about 50[Ω] (=1000/20). Moreover, in a case where the voltage ofthe signal SIGA is set to the low-level voltage VL (the voltage stateSL), the driver controller 27 respectively sets the signal PDA and thesignal PUA to “1” and “0”. This causes the pre-emphasis controller 28Ato set twenty of the signals PDA1 to PDA24 to “1”, and to set theremaining four of the signals PDA1 to PDA24 and the signals PUA1 toPUA24 to “0”. At this time, in the driver unit 29A, twenty of the twentyfour transistors 94 are turned on. As a result, the signal SIGA is setto the low-level voltage VL, and the output termination resistance(output impedance) of the driver unit 29A becomes about 50[Ω].

Further, in a case where the voltage state at the output terminal ToutAis set to the voltage state SM, the driver controller 27 sets both thesignal PUA and PDA to “1”. At this time, in a case where both thepre-emphasis control signals MUP2 and MDN2 are “0”, the pre-emphasiscontroller 28A sets ten of the signals PUA1 to PUA24 and ten of thesignals PDA1 to PDA24 to “1”, and sets the remaining fourteen of thesignals PUA1 to PUA24 and the remaining fourteen of the signals PDA1 toPDA24 to “0”. At this time, in the driver unit 29A, ten of the twentyfour transistors 91 are turned on, and ten of the twenty fourtransistors 94 to turned on. As a result, the signal SIGA is set to themedium-level voltage VM, and the output termination resistance (outputimpedance) of the driver unit 29A becomes about 50[Ω]. Furthermore, in acase where the pre-emphasis control signal MUP2 is “1”, and thepre-emphasis control signal MDN2 is “0”, the pre-emphasis controller 28Asets (10+m) of the signals PUA1 to PUA24 and (10−m) of the signals PDA1to PDA24 to “1”, and the remaining (14−m) of the signals PUA1 to PUA24and the remaining (14+m) of the signals PDAI to PDA24 to “0”. Herein,“m” is a natural number of 1 or more. At this time, in the driver unit29A, (10+m) of the twenty four transistors 91 are turned on, and (10−m)of the twenty four transistors 94 are turned on. As a result, the signalSIGA is set to a medium-level voltage VMplus that is slightly higherthan the medium-level voltage VM, and the output termination resistance(output impedance) of the driver unit 29A becomes about 50[Ω]. Moreover,in a case where the pre-emphasis control signal MDN2 is “1”, and thepre-emphasis control signal MUP2 is “0”, the pre-emphasis controller 28Asets (10−m) of the signals PDA1 to PUA24 and (10+m) of the signals PDA1to PDA24 to “1”, and sets the remaining (14+m) of the signals PUA1 toPUA24 and the remaining (14−m) of the signals PDA1 to PDA24 to “0”. Atthis time, in the driver unit 29A, (10−m) of the twenty four transistors91 are turned on, and (10+m) of the twenty four transistors 94 areturned on. As a result, the signal SIGA is set to a medium-level voltageVMminus that is slightly lower than the medium-level voltage VM, and theoutput termination resistance (output impedance) of the driver unit 29Abecomes about 50[Ω].

The driver controller 27 sets the voltage states at the output terminalsToutA., ToutB, and ToutC with use of the signals PUA, PDA, PUB, PDB,PUC, and PDC in such a manner. Moreover, the pre-emphasis controller 28Achanges the numbers of the transistors 91 and 94 to be turned on, on thebasis of the signals PUA and PDA and the pre-emphasis control signalsMUP2 and MDN2, to set the voltage level of the signal SIGA upon settingthe signal SIGA to the voltage state SM. Likewise, the pre-emphasiscontroller 28B changes the numbers of the transistors 91 and 94 to beturned on, on the basis of the signals PUB and PDB and the pre-emphasiscontrol signals MUP2 and MDN2, to set the voltage level of the signalSIGB upon setting the signal SIGB to the voltage state SM. Thepre-emphasis controller 28C changes the numbers of the transistors 91and 94 to be turned on, on the basis of the signals PUC and PDC and thepre-emphasis control signals MUP2 and MDN2, to set the voltage level ofthe signal SIGC upon setting the signal SIGC to the voltage state SM.

At this time, in a case where the symbol transition is the symboltransition having the possibility that the transition time of any of thedifferences AB, BC, and CA becomes long upon changing the signal SIGAfrom the voltage state SH or the voltage state SL to the voltage stateSM, the pre-emphasis controller 28A controls the driver unit 29A to setthe voltage of the signal SIGA to the medium-level voltage VMplus or themedium-level voltage VMminus, as will be described later. Likewise, in acase where the symbol transition is the symbol transition having thepossibility that the transition time of any of the differences AB, BC,and CA becomes long upon changing the signal SIGB from the voltage stateSH or the voltage state SL to the voltage state SM, the pre-emphasiscontroller 28B controls the driver unit 29B to set the voltage of thesignal SIGB to the medium-level voltage VMplus or the medium-levelvoltage VMminus. Moreover, in a case where the symbol transition is thesymbol transition having the possibility that the transition time of anyof the differences AB, BC, and CA becomes long upon changing the signalSIGC from the voltage state SH or the voltage state SL to the voltagestate SM, the pre-emphasis controller 28C controls the driver unit 29Cto set the voltage of the signal SIGC to the medium-level voltage VMplusand the medium-level voltage VMminus. This makes it possible to enhancecommunication performance in the communication system 1.

(Reception Device 30)

The reception device 30 includes a receiver 40 and a processor 32, asillustrated in FIG. 1.

The receiver 40 receives the signals SIGA, SIGB, and SIGC, and generatestransition signals RxF, RxR, and RxP and a clock signal RxCK on thebasis of the signals SIGA, SIGB, and SIGC.

FIG. 9 illustrates a configuration example of the receiver 40. Thereceiver 40 includes resistors 41A, 41B, and 41C, switches 42A, 42B, and42C, amplifiers 43A, 43B, and 43C, a clock generator 44, flip-flops 45and 46, and a signal generator 47.

The resistors 41A, 41B, and 41C each serve as a termination resistor inthe communication system 1, and have a resistance value of about 50[Ω]in this example. One end of the resistor 41A is coupled to the inputterminal TinA and is supplied with the signal SIGA, and the other endthereof is coupled to one end of the switch 42A. One end of the resistor41B is coupled to the input terminal TinB and is supplied with thesignal SIGB, and the other end thereof is coupled to one end of theswitch 42B. One end of the resistor 41C is coupled to the input terminalTinC and is supplied with the signal SIGC, and the other end thereof iscoupled to one end of the switch 42C.

The one end of the switch 42A is coupled to the other end of theresistor 41A, and the other end thereof is coupled to the other ends ofthe switches 42B and 42C. The one end of the switch 42B is coupled tothe other end of the resistor 41B, and the other end thereof is coupledto the other ends of the switches 42A and 42C. The one end of the switch42C is coupled to the other end of the resistor 41C, and the other endthereof is coupled to the other ends of the switches 42A and 42B. In thereception device 30, the switches 42A, 42B, and 42C are set to be on,and the resistors 41A to 41C serve as termination resistors.

A positive input terminal of the amplifier 43A is coupled to a negativeinput terminal of the amplifier 43C and the one end of the resistor 41Aand is supplied with the signal SIGA, and a negative input terminalthereof is coupled to a positive input terminal of the amplifier 43B andthe one end of the resistor 41B and is supplied with the signal SIGB.The positive input terminal of the amplifier 43B is coupled to thenegative input terminal of the amplifier 43A and the one end of theresistor 41B and is supplied with the signal SIGB, and a negative inputterminal thereof is coupled to a positive input terminal of theamplifier 43C and the one end of the resistor 41C and is supplied withthe signal SIGC. The positive input terminal of the amplifier 43C iscoupled to the negative input terminal of the amplifier 43B and the oneend of the resistor 41C and is supplied with the signal SIGC, and thenegative input terminal thereof is coupled to the positive inputterminal of the amplifier 43A and the resistor 41A and is supplied withthe signal SIGA.

With this configuration, the amplifiers 432A, 43B, and 43C respectivelyoutput a signal corresponding to the difference AB (SIGA−SIGB) betweenthe signal SIGA and the signal SIGB, a signal corresponding to thedifference BC (SIGB−SIGC) between the signal SIGB and the signal SIGC,and a signal corresponding to the difference CA (SIGC−SIGA) between thesignal SIGC and the signal SIGA.

FIG. 10 illustrates an example of the signals SIGA to SIGC to bereceived by the receiver 40. For convenience of description, FIG. 10illustrates waveforms in a case where the transmission device 10 doesnot perform a pre-emphasis operation. In this example, the receiver 40receives six symbols “+x”, “−y”, “−z”, “+z”, “'y”, and “−x” in thisorder. At this time, the voltage of the signal SIGA changes in order ofVH, VM, VH, VL, VM, and VL, the voltage of the signal SIGB changes inorder of VL, VM, VM, VH, and VH, and the voltage of the signal SIGCchanges in order of VM, VH, VL, VL, and VM. Accordingly, the differencesAB, BC, and CA also change. For example, the difference AB changes inorder of +2ΔV, +ΔV, +ΔV, −ΔV, −ΔV, and −2ΔV, the difference BC changesin order of −ΔV, −2ΔV, +ΔV, −ΔV, +2ΔV, and +ΔV, and the difference CAchanges in order of −ΔV, +ΔV, −2ΔV, +2ΔV, −ΔV, and +ΔV. Herein, ΔV is adifference between two adjacent voltages of the three voltages (thehigh-level voltage VH, the medium-level voltage VM, and the low-levelvoltage VL).

FIG. 11 illustrates an operation example of the amplifiers 43A, 43B, and43C in a case where the receiver 40 receives the symbol “+x”. It is tobe noted that the switches 42A, 42B, and 42C are on, and are not therebyillustrated. In this example, the signal SIGA is the high-level voltageVH, the signal SIGB is the low-level voltage VL, and the signal SIGC isthe medium-level voltage VM. In this case, a current Iin passes throughthe input terminal TinA, the resistor 41A, the resistor 41B, and theinput terminal TinB in this order. Thereafter, the positive inputterminal and the negative input terminal of the amplifier 43A arerespectively supplied with the high-level voltage VH and the low-levelvoltage VL to cause the difference AB to be positive (AB>0).Accordingly, the amplifier 32A outputs “1”. Moreover, the positive inputterminal and the negative input terminal of the amplifier 43B arerespectively supplied with the low-level voltage VL and the medium-levelvoltage VM to cause the difference BC to be negative (BC<0).Accordingly, the amplifier 43B outputs “0”. Further, the positive inputterminal and the negative input terminal of the amplifier 43C arerespectively supplied with the medium-level voltage VM and thehigh-level voltage VH to cause the difference CA to be negative (CA<0).Accordingly, the amplifier 43C outputs “0”.

The clock generator 44 generates the clock signal RxCK on the basis ofoutput signals of the amplifiers 43A, 43B, and 43C.

The flip-flop 45 delays the output signals of the amplifiers 43A, 43B,and 43C by one clock of the clock signal RxCK and outputs the respectiveoutput signals. The flip-flop 46 delays three output signals of theflip-flop 45 by one clock of the clock signal RxCK and outputs therespective output signals.

The signal generator 47 generates the transition signals RxF, RxR, andRxP on the basis of the output signals of the flip-flops 45 and 46 andthe clock signal RxCK. The transition signals RxF, RxR, and RxPrespectively correspond to the transition signals TxF, TxR, and TxP(FIG. 4) in the transmission device 10, and each indicate a symboltransition. The signal generator 47 specifies a symbol transition (FIG.3) on the basis of a symbol indicated by the output signals of theflip-flop 45 and a symbol indicated by the output signals of theflip-flop 46 to generate the transition signals RxF, RxR, and RxP.

The processor 32 (FIG. 1) performs predetermined processing on the basisof the transition signals RxF, RxR, and RxP and the clock signal RxCK.

Herein, the driver units 29A, 29B, and 29C correspond to specificexamples of a “driver unit” in the present disclosure. The signals SIGH,SIGB, and SIGC correspond to specific examples of a “data signal” in thepresent disclosure. The transition detector 25 and the pre-emphasiscontrollers 28A, 28B, and 28C correspond to specific examples of a“controller” in the present disclosure. The transmission symbolgenerator 22 corresponds to a specific example of a “signal generator”in the present disclosure. The transistor 91 and the resistor 92correspond to specific examples of a “first sub-circuit” in the presentdisclosure. The transistor 94 and the resistor 93 correspond to specificexamples of a “second sub-circuit” in the present disclosure.

[Operation and Workings]

Next, description is given of operation and workings of thecommunication system 1 according to the present embodiment.

(General Operation Outline)

First, a general operation outline of the communication system 1 isdescribed with reference to FIGS. 1, 4 and 7. The clock generator 11 ofthe transmission device 10 generates the clock signal TxCK. Theprocessor 12 performs predetermined processing to generate thetransition signals TxF0 to TxF6, TxR0 to TxR6, and TxP0 to TxP6. in thetransmitter 20 (FIG, 4), the serializer 21F generates the transitionsignal TxF9 on the basis of the transition signals TxF0 to TxF6 and theclock signal TxCK, the serializer 21R generates the transition signalTxR9 on the basis of the transition signal TxR0 to TxR6 and the clocksignal TxCK, and the serializer 21P generates the transition signal TxP9on the basis of the transition signal TxP0 to TxP6 and the clock signalTxCK. The transmission symbol generator 22 generates the symbol signalsTxl1, Tx2, and Tx3 on the basis of the transition signals TxF9, TxR9,and TxP9 and the clock signal TxCK. The transition detector 25 generatesthe pre-emphasis control signals MUP and MDN on the basis of thetransition signals TxF9, TxR9, and TxP9 and the symbol signals D1, D2,and D3.

In the output unit 26 (FIG. 7), the driver controller 27 generates thesignals PUA, PDA, PUB, PDB, PUC, and PDC on the basis of the symbolsignals Tx1, Tx2, and Tx3 and the clock signal TxCK. On the basis of thepre-emphasis control signals MUP and MDN and the clock signal TxCK, thetiming controller 27T performs timing adjustment on the pre-emphasiscontrol signal MUP to generate the pre-emphasis control signal MUP2, andperforms timing adjustment on the pre-emphasis control signal MDN togenerate the pre-emphasis control signal MDN2. The pre-emphasiscontroller 28A generates the signals PUA1 to PUA24 and PDA1 to PDA24 onthe basis of the signals PUA and PDA and the pre-emphasis controlsignals MUP2 and MDN2. The pre-emphasis controller 28B generates thesignals PUB1 to PUB24 and PDB1 to PDB24 on the basis of the signals PUBand PDB and the pre-emphasis control signals MUP2 and MDN2. Thepre-emphasis controller 28C generates the signals PUC1 to PUC24 and PDC1to PDC24 on the basis of the signals PUC and PDC and the pre-emphasiscontrol signals MUP2 and MDN2. The driver unit 29A generates the signalSIGA on the basis of the signals PUA1 to PUA24 and PDA1 to PDA24. Thedriver unit 29B generates the signal SIGB on the basis of the signalsPUB1 to PUB24 and PDB1 to PDB24. The driver unit 29C generates thesignal SAW on the basis of the signals PUC1 to PUC24 and PDC1 to PDC24.

In the reception device 30 (FIG. 1), the receiver 40 receives thesignals SIGA, SIGB, and SIGC, and generates the transition signals RxF,RxR, and RxP and the clock signal RxCK on the basis of the signals SIGA,SIGB, and SIGC. The processor 32 performs predetermined processing onthe basis of the transition signals RxF, RxR, and RxP and the clocksignal RxCK.

(Specific Operation)

Next, the operation of the transmission device 10 is described in detailbelow. In the transmission device 10, the transition detector 25generates the pre-emphasis control signals MUP and MDN on the basis ofthe transition signals TxF9, TxR9, and TxP9 and the symbol signals D1,D2, and D3. Specifically, the transition detector 25 confirms, on thebasis of the transition signals TxF9, TxR9, and TxP9 and the symbolsignals D1, D2, and D3, whether or not the symbol transition is thesymbol transition having the possibility that the transition time of anyof the differences AB, BC, and CA becomes long, and generates thepre-emphasis control signal MVP and MDN on the basis of a thus-obtainedresult.

FIG. 12 schematically illustrates eye diagrams of the differences AB,BC, and CA in a case where the transmission device 10 does not performpre-emphasis. As illustrated in FIG. 12, transitions W21 and W22 have alonger transition time than other transitions. The transition W21 is atransition from −2ΔV to +ΔV, and the transition W22 is a transition from+2ΔV to −ΔV.

The transition detector 25 confirms, on the basis of the transitionsignals TxF9, TxR9, and TxP9 and the symbol signals D1, D2, and D3,whether or not the symbol transition is the symbol transition, such asthe transitions W21 and W22, having the possibility that the transitiontime of any of the differences AB, BC, and CA becomes long. Thereafter,as illustrated in FIG. 5, in a case where the transition signals TxF9,TxR9, and TxP9 are “000” or “010”, the transition detector 25 determinesthat the symbol transition is the symbol transition having thepossibility that the transition time of any of the differences AB, BC,and CA becomes long. Thereafter, as illustrated by WUP circled by thesolid line in FIG. 5, in a case where the transition signals TxF9, TxR9,and TxP9 are “000” and the symbol DS indicated by the symbol signals D1,D2, and D3 is “+x”, “+y”, and “+z”, and in a case where the transitionsignals TxF9, TxR9, and TxP9 are “010” and the symbol DS indicated bythe symbol signals D1, D2, and D3 is “−x”, “−y”, and “−z”, thetransition detector 25 sets the pre-emphasis control signal MVP to “1”(active). Moreover, as illustrated by WDN circled by the broken line inFIG. 5, in a case where the transition signals TxF9, TxR9, and TxP9 are“000” and the symbol DS indicated by the symbol signals D1, D2, and D3is “−x”, “−y” and “−z”, and in a case where the transition signals TxF9,TxR9, and TxP9 are “010” and the symbol DS indicated by the symbolsignals D1, D2, and D3 is “+x”, “+y”, and “+z”, the transition detector25 sets the pre-emphasis control signal MDN to “1” (active).

Then, the pre-emphasis controller 28A sets the voltage of the signalSIGA to the medium-level voltage VMplus that is slightly higher than themedium-level voltage VM in a case where the pre-emphasis control signalMUP2 is “1”, and sets the voltage of the signal SIGA to the medium-levelvoltage VMminus that is slightly lower than the medium-level voltage VMin a case where the pre-emphasis control signal MDN2 is “1”. Likewise,the pre-emphasis controller 28B sets the voltage of the signal SIGB tothe medium-level voltage VMplus that is slightly higher than themedium-level voltage VM in the case where the pre-emphasis controlsignal MUP2 is “1”, and sets the voltage of the signal SIGB to themedium-level voltage VMminus that is slightly lower than themedium-level voltage VM in the case where the pre-emphasis controlsignal MDN2 is “1”. The pre-emphasis controller 28C sets the voltage ofthe signal SIGC to the medium-level voltage VMplus that is slightlyhigher than the medium-level voltage VM in the case where thepre-emphasis control signal MUP2 is “1”, and sets the voltage of thesignal SIGC to the medium-level voltage VMminus that is slightly lowerthan the medium-level voltage VM in the case where the pre-emphasiscontrol signal MDN2 is “1”.

FIGS. 13A to 13E illustrate an operation example of the communicationsystem 1 in a case where the symbol transits from “+x” to a symbol otherthan “−x”. FIG. 13A illustrates a case where the symbol transits from“+x” to “−x”, FIG. 13B illustrates a case where the symbol transits from“+x” to “+y”, FIG. 13C illustrates a case where the symbol transits from“+x” to “−y”, FIG. 13D illustrates a case where the symbol transits from“+x” to “+z”, and FIG. 13E illustrates a case where the symbol transitsfrom “+x” to “−z”. In each of FIGS. 13A to 13E, (A) indicates waveformsof the signals SIGA, SIGB, and SIGC at the output terminals ToutA,ToutB, and ToutC of the transmission device 10, and (B) indicateswaveforms of the differences AB, BC, and CA in the reception device 30.Moreover, a solid line indicates a waveform in a case where thepre-emphasis operation is performed, and a broken line indicates awaveform in a case where the pre-emphasis operation is not performed.

As illustrated in FIG. 5, in a case where the symbol DS is “+x” and thetransition signals TxF9, TxR9, and TxP9 are “1xx”, the symbol transitsfrom “+x” to “−x” (FIG. 13A). At this time, the transition detector 25sets both the pre-emphasis control signal MUP and MDN to “0” (inactive),as illustrated in FIG. 5. Accordingly, as illustrated in FIG. 13A, thesignal SIGA changes from the high-level voltage VH to the low-levelvoltage VL, the signal SIGB changes from the low-level voltage VL to thehigh-level voltage VH, and the signal SIGC maintains the medium-levelvoltage VM. In other words, in a case where the symbol transits from“+x” to “−x”, none of transitions of the differences AB, BC, and CAcorresponds to the transitions W21 and W22; therefore, the pre-emphasiscontroller 28C controls the driver unit 29C not to perform thepre-emphasis operation.

Moreover, in a case where the symbol DS is “+x” and the transitionsignals TxF9, TxR9, and TxP9 are “010”, the symbol transits from “+x” to“+y” (FIG. 13B). At this time, the transition detector 25 respectivelysets the pre-emphasis control signal MDN and the pre-emphasis controlsignal MUP to “1” (active) and “0” (inactive), as illustrated in FIG. 5.Accordingly, as illustrated in FIG. 13B, the signal SIGA changes fromthe high-level voltage VH to the medium-level voltage VM through themedium-level voltage VMminus, the signal SIGB changes from the low-levelvoltage VL to the high-level voltage VH, and the signal SIGC changesfrom the medium-level voltage VM to the low-level voltage VL. At thistime, the pre-emphasis controller 28A controls the driver unit 29A toset the voltage of the signal SIGA to the medium-level voltage VMminusthat is slightly lower than the medium-level voltage VM in a first halftime period (0.5 UI) of a time period in which the transmission device10 outputs the symbol “+y”. In other words, the transition of thedifference AB corresponds to the transition W22, and has a possibilitythat the transition time of the difference AB becomes long; therefore,the pre-emphasis controller 28A controls the driver unit 29A to performthe pre-emphasis operation.

Further, in a case where the symbol DS is “+x” and the transitionsignals TxF9, TxR9, and TxP9 are “011”, the symbol transits from “+x” to“−y” (FIG. 13C). At this time, the transition detector 25 sets both thepre-emphasis control signals MUP and MDN to “0” (inactive), asillustrated in FIG. 5. Accordingly, as illustrated in FIG. 13C, thesignal SIGA changes from the high-level voltage VH to the medium-levelvoltage VM, the signal SIGB maintains the low-level voltage VL, and thesignal SIGC changes from the medium-level voltage VM to the high-levelvoltage VH. In other words, in a case where the symbol transits from“+x” to “−y”, none of the transitions of the differences AB, BC, and CAcorresponds to the transitions W21 and W22; therefore, the pre-emphasiscontroller 28A controls the driver unit 29A not to perform thepre-emphasis operation.

Furthermore, in a case where the symbol DS is “+x” and the transitionsignals TxF9, TxR9, and TxP9 are “000”, the symbol transits from “±x” to“+z” (FIG. 13D). At this time, the transition detector 25 respectivelysets the pre-emphasis control signal MUP and the pre-emphasis controlsignal MDN to “1” (active) and “0” (inactive), as illustrated in FIG. 5.Accordingly, as illustrated in FIG. 13D, the signal SIGA changes fromthe high-level voltage VH to the low-level voltage VL, the signal SIGBchanges from the low-level voltage VL to the medium-level voltage VMthrough the medium-level voltage VMplus, and the signal SIGC changesfrom the medium-level voltage VM to the high-level voltage VH. At thistime, the pre-emphasis controller 28B controls the driver unit 29B toset the voltage of the signal SIGB to the medium-level voltage VMplusthat is slightly higher than the medium-level voltage VM in a first halftime period (0.5 UI) of a time period in which the transmission device10 outputs the symbol “+z”. In other words, the transition of thedifference AB corresponds to the transition W22, and has a possibilitythat the transition time of the difference AB becomes long; therefore,the pre-emphasis controller 28B controls the driver unit 29B to performthe pre-emphasis operation.

Moreover, in a case where the symbol DS is “+x” and the transitionsignals TxF9, TxR9, and TxP9 are “001”, the symbol transits from “+x” to“−z” (FIG. 13E). At this time, the transition detector 25 sets both thepre-emphasis control signals MUP and MDN to “0” (inactive), asillustrated in FIG. 5. Accordingly, as illustrated in FIG. 13E, thesignal SIGA maintains the high-level voltage VH, the signal SIGB changesfrom the low-level voltage VL to the medium-level voltage VM, and thesignal SIGC changes from the medium-level voltage VM to the low-levelvoltage VL. In other words, in a case where the symbol transits from“+x” to “−z”, none of the transitions of the differences AB, BC, and CAcorresponds to the transitions W21 and W22, therefore, the pre-emphasiscontroller 28B controls the driver unit 29B not to perform thepre-emphasis operation.

It is to be noted that the case where the symbol transits from “+x” to asymbol other than “+x” is described in this example; however, this alsoapplies a case where the symbol transits from “−x” to a symbol otherthan “−x”, a case where the symbol transits from “+y” to a symbol otherthan “+y”, a case where the symbol transits from “−y” to a symbol otherthan “−y”, a case where the symbol transits from “+z” to a symbol otherthan “+z”, and a case where the symbol transits from “−z” to a symbolother than “−z”.

As described above, in the communication system 1, for example, in acase where the symbol transition is a symbol transition having thepossibility that the transition time of any of the differences AB, BC,and CA becomes long upon changing the signal SIGA from the voltage stateSH or the voltage state SL to the voltage state SM, the driver unit 29Aperforms the pre-emphasis operation. This makes it possible to enhancewaveform quality in the communication system 1, for example, in a casewhere the transmission path 100 is long. In particular, in thetransmission device 10, even in a case where the medium-level voltagesVMplus and VMminus are outputted, the output impedances of the driverunits 29A, 29B, and 29C become about 50[Ω], which makes it possible toenhance waveform quality. As a result, it is possible to enhancecommunication performance in the communication system 1.

Moreover, in the communication system 1, the transition detector 25detects a specific symbol transition on the basis of the transitionsignals TxF9, TxR9, and TxP9, and the pre-emphasis controllers 28A, 28B,and 28C cause the driver units 29A, 29B, and 29C to perform thepre-emphasis operation on the basis of a thus-obtained detection result.This makes it possible to actively perform the pre-emphasis operationon, for example, only the symbol transition having a possibility thatwaveform quality is deteriorated in the communication system 1, whichmakes it possible to effectively enhance waveform quality.

FIGS. 14A to 14D illustrate eye diagrams of the difference AB betweenthe signal SIGA and the signal SIGB, the difference BC between thesignal SIGB and the signal SIGC, and the difference CA between thesignal SIGC and the signal SIGA in the communication system 1. In a casewhere the voltage state at the output terminal ToutA is set to thevoltage state SM, the driver unit 29A turns on, for example, (10+m)transistors 91 and (10−m) transistor 94 to set the signal SIGA to themedium-level voltage VMplus, and turns on (10−m) transistors 91 and(10+m) transistors 94 to set the signal SIGA to the medium-level voltageVMminus. FIG. 14A illustrates a case of “m=0”, FIG. 14B illustrates acase of “m=1”, FIG. 14C illustrates a case of “m=2”, and FIG. 14Dillustrates a case of “m=3”. “m=0” indicates that the pre-emphasisoperation is not performed. With an increase in the value of “m”, themedium-level voltage VMplus becomes higher and the medium-level voltageVMminus becomes lower. In other words, a deviation amount (a boostamount) of the medium-level voltage VM by the pre-emphasis operationbecomes larger with an increase in the value of “m”. Accordingly, it ispossible to widen an eye opening with an increase in the value of “m”,as illustrated in FIGS. 14A to 14D. As described above, in thecommunication system 1, performing the pre-emphasis operation makes itpossible to widen the eye opening, and as a result, it is possible toenhance communication performance.

(Comparative Example)

Next, workings of the present embodiment are described as compared witha comparative example. A communication system 1R according to thecomparative example includes a transmission device 10R. The transmissiondevice 10R includes two driver units 29RA that both are coupled to theoutput terminal ToutA, two driver units 29RB that both are coupled tothe output terminal ToutB, and two driver units 29RC that both arecoupled to the output terminal ToutC. For example, the transmissiondevice 10R causes the two driver unit 29RA to operate together, therebycausing the output impedance to become about 25[Ω], causes the twodriver units 29RB to operate together, thereby causing the outputimpedance to become about 25[Ω], and causes the two driver unit 29RC tooperate together, thereby causing the output impedance to become about25[Ω]. The transmission device 10R reduces the output impedance in sucha manner to perform the pre-emphasis operation.

FIGS. 15A to 15E illustrate an operation example of the communicationsystem IR in a case where the symbol transits from “+x” to a symbolother than “'x”. For example, as illustrated in FIG. 15A, in a casewhere the symbol transits from “+x” to “+x”, the signal SIGA changesfrom the high-level voltage VH to the low-level voltage VL through avoltage lower than the low-level voltage VL, the signal SIGB changesfrom the low-level voltage VL to the high-level voltage VH through avoltage higher than the high-level voltage VH, and the signal SIGCmaintains the medium-level voltage VM. At this time, in a first halftime period (0.5 UI) of a time period in which the transmission device10R outputs the symbol “−x”, both the two driver units 29RA operate tocause the output impedance to become about 25[Ω], both the two driverunits 29RB operate to cause the output impedance to become about 25[Ω],and both the two driver units 29RC operate to cause the output impedanceto become about 25[Ω]. This also applies other symbol transitions.

As described above, in the communication system 1R according to thecomparative example, the output impedance is set to about 25[Ω] toperform the pre-emphasis operation, which causes a time period in whichthe output impedance does not match a characteristic impedance of thetransmission path 100. Accordingly, in the communication system 1R,there is a possibility that waveform quality is deteriorated todeteriorate communication performance. Moreover, in the communicationsystem 1R, the output impedance transiently becomes about 25[Ω] uponoutputting the median-level voltage VM, which increases a DC current byThevenin termination, and as a result, power consumption related to theCD current is increased by about 67%, for example. Further, in thecommunication system 1R, the two driver units 29RA, the two driver units29RB, and the two driver units 29RC are provided, which increases acircuit area.

In contrast, in the communication system 1 according to the presentembodiment, the numbers of the transistors 91 and 94 to be turned on arechanged to perform the pre-emphasis operation, which makes it possibleto maintain the output impedance at about 50[Ω]. As a result, the outputimpedance matches the characteristic impedance of the transmission path100, which makes it possible to enhance waveform quality and enhancecommunication performance. Moreover, in the communication system 1, ascompared with the communication system 1R according to the comparativeexample, it is possible to reduce the DC current by Thevenintermination, which makes it possible to reduce power consumption.Further, in the communication system 1, one driver unit 29A, one driverunit 29B, and one driver unit 29C are provided, which makes it possibleto reduce a circuit area, as compared with the communication system 1Raccording to the comparative example.

[Effects]

As described above, in the present embodiment, in the case where thesymbol transition is the symbol transition having the possibility thatthe transition time of any of the differences AB, BC, and CA becomeslong, the driver unit that outputs the medium-level voltage after thetransition performs the pre-emphasis operation. In particular, even in acase where the medium-level voltage VMplus and VMminus are outputted,the output impedance becomes about 50[Ω], which makes it possible toenhance communication performance and reduce power consumption.

In the present embodiment, the transition detector detects a specificsymbol transition on the basis of the transition signal, and thepre-emphasis controller causes the driver unit to perform thepre-emphasis operation on the basis of a thus-obtained detection result,which makes it possible to effectively enhance communicationperformance.

[Modification Example 1-1]

In the foregoing embodiment, twenty transistors 91 are turned on togenerate the high-level voltage VH; however, the embodiment is notlimited thereto. For example, in a case where the sum of the resistancevalue of on resistance of the transistor 91 and the resistance value ofthe resistor 92 is smaller than 1000[Ω] by device variations inmanufacturing, the number of the transistors 91 to be turned on may bereduced. Moreover, in a case where the sum of the resistance value of onresistance of the transistor 91 and the resistance value of the resistor92 is larger than 1000[Ω], the number of the transistors 91 to be turnedon may be increased. This also applies to a case where the low-levelvoltage VL is generated.

[Modification Example 1-2]

In the foregoing embodiment, ten transistors 91 and ten transistors 94are turned on to generate the medium-level voltage VM; however, theembodiment is not limited thereto. For example, in a case where the sumof the resistance value of on resistance of the transistor 91 and theresistance value of the resistor 92 is smaller than the sum of theresistance value of on resistance of the transistor 94 and theresistance value of the resistor 93 by device variations inmanufacturing, a number M1 of the transistors 91 to be turned on may besmaller than a number M2 of the transistors 94 to be turned on.Moreover, in a case where the sum of the resistance value of onresistance of the transistor 91 and the resistance value of the resistor92 is larger than the sum of the resistance value of on resistance ofthe transistor 94 and the resistance value of the resistor 93, thenumber M1 of the transistors 91 to be turned on may be larger than thenumber M2 of the transistors 94 to be turned on. This makes it possibleto bring the medium-level voltage VM close to a medium voltageinterposed between the high-level voltage VH and the low-level voltageVL.

Likewise, in the foregoing embodiment, (10+m) transistors 91 and (10−m)transistors 94 are turned on to generate the medium-level voltageVMplus, and (10−m) transistors 91 and (10+m) transistors 94 are turnedon to generate the medium-level voltage VMminus; however, the embodimentis not limited thereto. Alternatively, for example, (M1+m1) transistors91 and (M2−m2) transistors 94 may be turned on to generate themedium-level voltage VMplus, and (M1−m1) transistors 91 and (M2+m2)transistors 94 may be turned on to generate the medium-level voltageVMminus.

[Modification Example 1-3]

In the foregoing embodiment, the pre-emphasis control signals MUP2 andMDN2 are changeable from the low level to the high level at the starttiming of the unit interval UI, and are changeable from the high levelto the low level at a timing after a lapse of a half time period (0.5UI) of the unit interval UI from the start timing of the unit intervalUI, as illustrated in FIG. 8; however, the embodiment is not limitedthereto. Alternatively, for example, the pre-emphasis control signalsMUP2 and MDN2 may be changeable from the low level to the high level atthe start timing of the unit interval UI, and may be changeable from thehigh level to the low level at a timing after a lapse of a time periodshorter than a half of the unit interval UI from the start timing of theunit interval UI. Moreover, for example, the pre-emphasis controlsignals MUP2 and MDN2 may be changeable from the low level to the highlevel at the start timing of the unit interval UI, and may be changeablefrom the high level to the low level at a timing after a lapse of a timeperiod longer than the half of the unit interval UI from the starttiming of the unit interval UI.

[Modification Example 1-4]

In the foregoing embodiment, the numbers of the transistors 91 and 94are changed to generate the medium-level voltages VMplus and VMminushowever, the embodiment is not limited thereto. The present modificationexample is described in detail below.

FIG. 16 illustrates a configuration example of an output unit 26Aaccording to the present modification example. The output unit 26includes the driver controller 27, the timing controller 27T, impedancecontrollers 18A, 18B, and 18C, an operational amplifier 14, a capacitor15, and driver units 19A, 19B, and 19C.

The impedance controller 18A generates signals PUA1 to PUA24, PDA1 toPDA24, and PMA on the basis of the signal PUA and PDA. Specifically, ina case where the signal PUA is “1” and the signal PDA is “0”, theimpedance controller 18A sets twenty of the signals PUA1 to PUA24 to “1”and sets the remaining four of the signals PUA1 to PUA24, the signalsPDA1 to PDA24, and the signal PMA to “0”. Moreover, in a case where thesignal PDA is “1” and the signal PUA is “0”, the impedance controller18A sets twenty of the signals PDA1 to PDA24 to “1”, and sets theremaining four of the signals PDA1 to PDA24, the signals PUA1 to PUA24,and the signal PMA to “0”. Further, in a case where both the signals PUAand PDA are “0”, the impedance controller 18A sets the signal PMA to“1”, and sets the signal PUA1 to PUA24 and PDA1 to PDA24 to “0”.

Likewise, the impedance controller 183 generates signals PUB1 to PUB24,PDB1 to PDB24, and PMB on the basis of the signals PUB and PDB.Moreover, the impedance controller 18C generates signals PUC1 to PUC24,PDC1 to PDC24, and PMC on the basis of the signals PUC and PDC.

A positive input terminal of the operational amplifier 14 is suppliedwith the medium-level voltage VM, and a negative input terminal thereofis coupled to an output terminal thereof. With this configuration, theoperational amplifier 14 operates as a voltage follower, and outputs themedium-level voltage VM to supply the medium-level voltage VM to thedriver units 19A, 19B, and 19C. One end of the capacitor 15 is coupledto the output terminal of the operational amplifier 14, and the otherend thereof is grounded.

The driver unit 19A generates the signal SIGA on the basis of thesignals PUA1 to PUA24, PDA1 to PDA24, and PMA and the pre-emphasiscontrol signals MUP2 and MDN2. The driver unit 19B generates the signalSIGB on the basis of the signals PUB1 to PUB24, PDB1 to PDB24, and PMBand the pre-emphasis control signals MUP2 and MDN2. The driver unit 19Cgenerates the signal SIGC on the basis of the signals PUC1 to PUC24,PDC1 to PDC24, and PMC and the pre-emphasis control signals MUP2 andMDN2.

FIG. 17 illustrates a configuration of the driver unit 19A. It is to benoted that this also applies to the driver units 19B and 19C. The driverunit 19A includes the drivers 29A1 to 29A24 and a driver 16A. The driver16A includes current sources 101 and 104, transistors 102, 103, and 106,and a resistor 105. One end of the current source 101 is supplied withthe age V1, the other end thereof is coupled to a drain of thetransistor 102. One end of the current source 104 is coupled to a sourceof the transistor 103, and the other end thereof is grounded. Thetransistors 102 and 103 in this example are N-channel MOS-FETs. A gateof the transistor 102 is supplied with the pre-emphasis control signalMUP2, the drain thereof is coupled to the other end of the currentsource 101, and a source thereof is coupled to a drain of the transistor103, the other end of the resistor 105, and a source of the transistor106. A gate of the transistor 103 is supplied with the pre-emphasiscontrol signal MDN2, the source thereof is coupled to the one end of thecurrent source 104, and the drain thereof is coupled to the source ofthe transistor 102, the other end of the resistor 105, and the source ofthe transistor 106. The resistor 105 serve as an output terminationresistor in a case where the signal SIGA is set to the voltage state SM,and a resistance value thereof is about 50[Ω]. One end of the resistor105 is supplied with the medium-level voltage VM by the operationalamplifier 14, and the other end thereof is coupled to the sources of thetransistors 102 and 106 and the drain of the transistor 103. Thetransistor 106 in this example is an N-channel MOS-FET. A gate of thetransistor 106 is supplied with the signal PMA, the source thereof iscoupled to the source of the transistor 102, the drain of the transistor103, and the other end of the resistor 105, and a drain thereof iscoupled to the output terminal ToutA.

Herein, the operational amplifier 14, the capacitor 15, and the driver16A correspond to specific examples of a “third circuit” in the presentdisclosure.

With this configuration, for example, in a case where the voltage of thesignal SIGA is set to the high-level voltage VH (the voltage state SH),in the driver unit 19A, twenty of the twenty four transistors 91 areturned on, and the remaining four of the twenty four transistors 91, thetwenty four transistors 94, and the transistor 106 are turned off. As aresult, the signal SIGA is set to the high-level voltage VH, and theoutput termination resistance (output impedance) of the driver unit 19Abecomes about 50[Ω](=1000/20). Moreover, in a case where the voltage ofthe signal SIGA is set to the low-level voltage VL (the voltage stateSL), in the driver unit 19A, twenty of the twenty four transistors 94are turned on, and the remaining four of the twenty four transistors 94,the twenty four transistors 91, and the transistor 106 are turned off.As a result, the signal SIGA is set to the low-level voltage VL, and theoutput termination resistance (output impedance) of the driver unit 19Abecomes about 50[Ω].

Further, in a case where the voltage state at the output terminal ToutAis set to the voltage state SM, in the driver unit 19A, the transistor106 is turned on, and the twenty four transistors 91 and the twenty fourtransistors 94 are turned off. At this time, in a case where both thepre-emphasis control signals MUP2 and MDN2 are “0”, the transistors 102and 103 are turned off. Accordingly, the signal SIGA is set to themedium-level voltage VM, and the output termination resistance (outputimpedance) of the driver unit 29A becomes about 50[Ω]. Furthermore, in acase where pre-emphasis control signal MUP2 is “1” and the pre-emphasiscontrol signal MDN2 is “0”, the transistor 102 is turned on, and thetransistor 103 is turned off. Accordingly, a current passes through thecurrent source 101, the transistor 102, and the resistor 105 in thisorder, and as a result, the signal SIGA is set to the medium-levelvoltage VMplus that is slightly higher than the medium-level voltage VM.At this time, the output termination resistance (output impedance) ofthe driver unit 29A is about 50[Ω]. Moreover, in a case where thepre-emphasis control signal MDN2 is “1” and the pre-emphasis controlsignal MUP2 is “0”, the transistor 103 is turned on, and the transistor102 is turned off. Accordingly, a current passes through the resistor105, the transistor 103, and the current source 104 in this order, andas a result, the signal SIGA is set to the medium-level voltage VMminusthat is slightly lower than the medium-level voltage VM. At this time,the output termination resistance (output impedance) of the driver unit29A is about 50[Ω].

Even such a configuration makes it possible to achieve effects similarto those in the foregoing embodiment.

[Other Modification Example]

Moreover, two or more of these modification examples may be combined.

<2. Second Embodiment>

Next, description is given of a communication system 2 according to asecond embodiment. In the present embodiment, a driver unit that outputsthe high-level voltage VH or the low-level voltage VL after thetransition also performs the pre-emphasis operation. It is to be notedthat components substantially same as those of the communication system1 according to the foregoing first embodiment are denoted by the samereference numerals, and description of such components is appropriatelyomitted.

The communication system 2 includes a transmission device 50, asillustrated in FIG. 1. The transmission device 50 includes a transmitter60. The transmitter 60 includes an output unit 66, as illustrated inFIG. 4.

FIG. 18 illustrates a configuration example of the output unit 66. Theoutput unit 66 includes the driver controller 27, the timing controller27T, pre-emphasis controllers 68A, 68B, and 68C, and driver units 69A,69B, and 69C.

The pre-emphasis controller 68A generates eight signals PUAA0, PUAB0,PUAA1, PUAB1, PDAA0, PDAB1, PDAA1, and PDAB1 on the basis of the signalsPUA and PDA and the pre-emphasis control signals MUP2 and MDN2. Thedriver unit 69A generates the signal SIGA on the basis of the eightsignals PUBA0, PUAB0, PUAA1, PUAB1, PDAA0, PDAB0, PDAA1, and PDAB1.

The pre-emphasis controller 68B generates eight signals PUBA0, PUBB0,PUBA1, PUBB1, PDBA0, PDAB0, PDBA1, and PDBB1 on the basis of the signalsPUB and PDB and the pre-emphasis control signals MUP2 and MDN2. Thedriver unit 69B generates the signal SIGB on the basis of the eightsignals PUBB0, PUBB0, PUBA1, PUBB1, PDBA0, PUBB0, PDBA1, and PDBB1.

The pre-emphasis controller 68C generates eight signals PUCB0, PUCB0,PUCA1, PUCB1, PDCA0, PDCB0, PDCA1, and PDCB1 on the basis of the signalsPUC and PDC and the pre-emphasis control signals MUP2 and MDN2. Thedriver unit 69C generates the signal SIGC on the basis of the eightsignals PUCA0, PUCB0, PUCA1, PUCB1, PDCA0, PDCB0, PDCA1, and PDCB1.

FIG. 19 illustrates a configuration example of the driver unit 69A. Itis to be noted that this also applies to the driver units 19B and 19C,The driver unit 69A includes M circuits UA0 (circuits UA0 ₁ to UA0_(M)), N circuits UB0 (circuits UB0 ₁ to UB0 _(N)), M circuits UA1(circuits UA1 ₁ to UA1 _(M)), N circuits UB1 (circuits UB1 ₁ to UB1_(N)), M circuits DA0 (circuits DA0 ₁ to DA0 _(M)), N circuits DB0(circuits DB0 ₁ to DB0 _(N)), M circuits DA1 (circuits DA1 ₁ to DA1_(M)), and N circuits DB1 (circuits DB1 ₁ to DB1 _(N)). Herein, “M” is anumber larger than “N”.

Each of the circuits UA0 ₁ to UA0 _(M), UB0 ₁ to UB0 _(N), UA1 ₁ to UA1_(M), and UB1 ₁ to UB1 _(N) includes the transistor 91 and the resistor92. A gate of the transistor 91 in each of the circuits UA0 ₁ to UA0_(M) is supplied with the signal PUAA0. A gate of the transistor 91 ineach of the circuits UB0 ₁ to UB0 _(N) is supplied with the signalPUAB0. A gate of the transistor 91 in each of the circuits UA1 ₁ to UA1_(M) is supplied with the signal PUAA1. A gate of the transistor 91 ineach of the circuits UB1 ₁ to UB1 _(N) is supplied with the signalPUAB1.

Each of the circuits DA0 ₁ to DA0 _(M), DB0 ₁ to DB0 _(N), DA1 ₁ to DA1_(M), DB1 ₁ to DB1 _(N) includes the resistor 93 and the transistor 94.A gate of the transistor 94 in each of the circuits DA0 ₁ to DA0 _(M) issupplied with the signal PDAA0. A gate of the transistor 94 in each ofthe circuits DB0 ₁ to DB0 _(N) is supplied with the signal PDAB0. A gateof the transistor 94 in each of the circuits DA1 ₁ to DA1 _(M) issupplied with the signal PDAA1. A gate of the transistor 94 in each ofthe circuits DB1 ₁ to DB1 _(N) is supplied with the signal PDAB1.

FIG. 20 illustrates an operation example of the pre-emphasis controller68A and the driver unit 69A. It is to be noted that this also applies tothe pre-emphasis controller 68B and the driver unit 69B, and alsoapplies to the pre-emphasis controller 68C and the driver unit 69C.Herein, it is indicated that “X” may be either “0” or “1”.

For example, in a case where the signals PUA and PDA are “10” and thepre-emphasis control signals MUP2 and MDN2 are “0X”, the pre-emphasiscontroller 68A sets the signals PUAA0, PUAB0, PDAA1, PUAB1, PDAA0,PDAB0, PDAA1, and PDAB1 to “11110000”. Accordingly, in the driver unit69A, the transistors 91 in the circuits UA0 ₁ to UA0 _(M), UB0 ₁ to UB0_(N), UA1 ₁ to UA1 _(M), and UB1 ₁ to UB1 _(N) are turned on. As a resthe signal SIGA is set to the high-level voltage VH, and the outputtermination resistance (output impedance) of the driver unit 69A becomesabout 50[Ω].

Moreover, for example, in a case where the signals PUA and PDA are “10”and the pre-emphasis control signals MUP2 and MDN2 are “10”, thepre-emphasis controller 68A sets to the signals PDAA1, PUAB1, PUAA1,PUAB1, PDAA1, PDAB0, PDAA1, and PDAB1 to “10110001”. Accordingly, in thedriver unit 69A, the transistors 91 in the circuits UA0 ₁ to UA0 _(M),UA1 ₁ to UA1 _(M), and UB1 ₁ to UB1 _(N) are turned on, and thetransistors 94 in the circuits DB1 ₁ to DB1 _(N) are turned on. As aresult, the signal SIGA is set to a high-level voltage VHminus that isslightly lower than the high-level voltage VH, and the outputtermination resistance (output impedance) of the driver unit 69A becomesabout 50[Ω].

Further, for example, in a case where the signals PUA and PDA are “11”and the pre-emphasis control signals MUP2 and MDN2 are “10”, thepre-emphasis controller 68A sets the signals PUAA0, PUAB0, PUAA1, PUAB1,PDAA0, PDAB0, PDAA1, and PDAB1 to “11011000”. Accordingly, in the driverunit 69A, the transistors 91 in the circuits UA0 ₁ to UA0 _(M), UB0 ₁ toUB0 _(N), and UB1 ₁ to UB1 _(N) are turned on, and the transistor 94 inthe circuits DA0 ₁ to DA0 _(M) are turned on. As a result, the signalSIGA is set to the medium-level voltage VMplus that is slightly higherthan the medium-level voltage VM, and the output termination resistance(output impedance) of the driver unit 69A becomes about 50[Ω].

Furthermore, for example, in a case where the signals PUA and PDA are“11” and the pre-emphasis control signals MUP2 and MDN2 are “00”, thepre-emphasis controller 68A sets the signals PUAA0, PUAB0, PUAA1, PDAB1,PDAA0, PDAB0, PDAA1, and PDAB1 to “11001100”. Accordingly, in the driverunit 69A, the transistors 91 in the circuits UA0 ₁ to UA0 _(M) and UB0 ₁to UB0 _(N) are turned on, and the transistors 94 in the circuits DA0 ₁to DA0 _(M) and DB0 ₁ to DB0 _(N) are turned on. As a result, the signalSIGA is set to the medium-level voltage VM, and the output terminationresistance (output impedance) of the driver unit 69A becomes about50[Ω].

Moreover, for example, in a case where the signals PUA and PDA are “11”and the pre-emphasis control signals MUP2 and MDN2 are “01”, thepre-emphasis controller 68A sets the signals PUAA0, PUAB0, PUAA1, PDAB1,PDAA0, PDAB0, PDAA1 and PDAB1 to “10001101”. Accordingly, in the driverunit 69A, the transistors 91 in the circuits UA0 ₁ to UA0 _(M) areturned on, and the transistor 94 in the circuits DA0 ₁ to DA0 _(M), DB0₁ to DB0 _(N), and DB1 ₁ to DB1 _(N) are turned on. As a result, thesignal SIGA is set to the medium-level voltage VMminus that is slightlylower than the medium-level voltage VM, and the output terminationresistance (output impedance) of the driver unit 69A becomes about50[Ω].

Further, for example, in a case where the signals PUA and PDA are “01”and the pre-emphasis control signals MUP2 and MDN2 are “01”, thepre-emphasis controller 684 sets the signals PUAA0, PUAB0, PUAA1, PUAB1,PDAA0, PDAB0, PDAA1, and PDAB1 to “01001110”. Accordingly, in the driverunit 69A, the transistors 91 in the circuits UB0 ₁ to UB0 _(N) areturned on, and the transistor 94 in the circuits DA0 ₁ to DA0 _(M), DB0₁ to DB0 _(N), and DA1 ₁ to DA1 _(M) are turned on. As a result, thesignal SIGA is set to a low-level voltage VLplus that is slightly higherthan the low-level voltage VL, and the output termination resistance(output impedance) of the driver unit 69A becomes about 50[Ω].

Furthermore, for example, in a case where the signals PUA and PDA are“01” and the pre-emphasis control signals MUP2 and MDN2 are “X0”. thepre-emphasis controller 68A sets the signals PUAA0, PUAB0, PUAB1, PUAB1,PDAA0, PDAB0, PDAA1, and PUAB1 to “00001111”. Accordingly, in the driverunit 69A, the transistors 94 in the circuits DA0 ₁ to DA0 _(M), DB0 ₁ toDB0 _(N), DA1 ₁ to DA1 _(M), and DB1 ₁ to DB1 _(N) are turned on. As aresult, the signal SIGA is set to the low-level voltage VL, and theoutput termination resistance (output impedance) of the driver unit 69Abecomes about 50[Ω].

Herein, the circuits UA0 ₁ to UA0 _(M), UB0 ₁ to UB0 _(N), UA1 ₁ to UA1_(M), and UB1 ₁ to UB1 _(N) correspond to a specific example of a“plurality of first sub-circuits” in the present disclosure. Thecircuits DA0 ₁ to DA0 _(M), DB0 ₁ to DB0 _(N), DA1 ₁ to DA1 _(M), andDB1 ₁ to DB1 _(N) correspond to a specific example of a “plurality ofsecond sub-circuits” in the present disclosure.

FIGS. 21A, 21B, and 21C illustrate an operation example of the driverunit 69A upon outputting the symbol “−z”. FIG. 21A illustrates a casewhere the pre-emphasis control signals MUP2 and MDN2 are “00”, FIG. 21Billustrates a case where the pre-emphasis control signals MUP2 and MDN2are 10″, and FIG. 21C illustrates a case where the pre-emphasis controlsignals MUP2 and MDN2 are “01”. In FIGS. 21A, 219, and 21C, a circuitindicated by a solid line and a circuit indicated by a broken line ofthe circuits UA0 ₁ to UA0 _(M), UB0 ₁ to UB0 _(N), UA1 ₁, to UA1 _(M),and UB1 ₁ to UB1 _(N) respectively indicate a circuit in which thetransistor 91 is turned on, and a circuit in which the transistor 91 isturned off. Likewise, a circuit indicated by a solid line and a circuitindicated by a broken line of the circuits DA0 ₁ to DA0 _(M), DB0 ₁ toDB0 _(N), DA1 ₁ to DA1 _(M), and DB1 ₁ to DB1 _(N) respectively indicatea circuit in which the transistor 94 is turned on, and a circuit inwhich the transistor 94 is turned off.

In the case where the pre-emphasis control signals MUP2 and MDN2 are“00”, in the driver unit 69A, the transistors 91 in the M circuits UA0,the N circuits UB0, the M circuits UA1, and the N circuits UB1 areturned on, as illustrated in FIG. 21A. Moreover, in the driver unit 69B,the transistors 91 in the M circuits UA0 and the N circuits UB0 areturned on, and the transistors 94 in the M circuits DA0 and the Ncircuits DB0 are turned on. Further, in the driver unit 69C, thetransistors 94 in the M circuits DA0, the N circuits DB0, the M circuitsDA1, and the N circuits DB1 are turned on. Accordingly, the voltage ofthe signal SIGA is set to the high-level voltage VH, the voltage of thesignal SIGB is set to the medium-level voltage VM, and the voltage ofthe signal SIGC is set to the low-level voltage VL.

In the case where the pre-emphasis control signals MUP2 and MDN2 are“10”, in the driver unit 69A, the transistors 91 in the M circuits UA0,the M circuits UA1, and the N circuits UB1 are turned on, and thetransistors 94 in the N circuits DB1 are turned on, as illustrated inFIG. 21B. Moreover, in the driver unit 69B, the transistor 91 in the Mcircuits UA0, the N circuits UB0, and the N circuits UB1 are turned on,and the transistors 94 in the M circuits DA0 are turned on. Further, inthe driver unit 69C, the transistors 94 in the M circuits DA0, the Ncircuits DB0, the M circuits DA1, and the N circuits DB1 are turned on.Accordingly, the voltage of the signal SIGA is set to the high-levelvoltage VHminus that is slightly lower than the high-level voltage VH,the voltage of the signal SIGB is set to the medium-level voltage VMplusthat is slightly higher than the medium-level voltage VM, and thevoltage of the signal SIGC is set to the low-level voltage VL. In otherwords, the driver unit 69A turns off the transistors 91 in the Ncircuits UB0 and turns on the transistors 94 in the N circuits DB1 todecrease the voltage of the signal SIGA from the high-level voltage VHto the high-level voltage VHminus, as compared with the case in FIG.21A. Moreover, the driver unit 69B turns on the transistors in the Ncircuits UB1. and turns off the transistors 94 in the N circuits DB0 toincrease the voltage of the signal SIGB from the medium-level voltage VMto the medium-level voltage VMplus, as compared with the case in FIG.21A.

In a case where the pre-emphasis control signals MUP2 and MDN2 are “01”,in the driver unit 69A, the transistors 91 in the M circuits UA0, the Ncircuits UB0, the M circuits UA1, and the N circuits UB1 are turned on,as illustrated in FIG. 21C. Moreover, in the driver unit 69B, thetransistors 91 in the M circuits UA0 are turned on, and the transistors94 in the M circuits DA0, the N circuits DB, the N circuits DB1 areturned on. Further, in the driver unit 69C, the transistors 91 in the Ncircuits UB0 are turned on, and the transistors 94 in the M circuitsDA0, the N circuits DB0, and the M circuits DA1 are turned on.Accordingly, the voltage of the signal SIGA is set to the high-levelvoltage VH, the voltage of the signal SIGB is set to the medium-levelvoltage VMminus that is slightly lower than the medium-level voltage VM,and the voltage of the signal SIGC is set to the low-level voltageVLplus that is slightly higher than the low-level voltage VL. In otherwords, the driver unit 69B turns off the transistors 91 in the Ncircuits UB0, and turns on the transistors 94 in the N circuits DB1 todecrease the voltage of the signal SIGB from the medium-level voltage VMto the medium-level voltage VMminus, as compared with the case in FIG.21A. Moreover, the driver unit 69C turns on the transistors 91 in the Ncircuits UB0, and turns off the transistors 94 in the N circuits DB1 toincrease the voltage of the signal SIGC from the low-level voltage VL tothe low-level voltage VLplus, as compared with the case in FIG. 21A.

FIGS. 22A to 22E illustrate an operation example of the communicationsystem 2 in a case where the symbol transits from “+x” to a symbol otherthan “+x”.

As illustrated in FIG. 5, in a case where the symbol DS is “+x”, and thetransition signals TxF9, TxR9, and TxP9 are “1xx”, the symbol transitsfrom “+x” to “−x” (FIG. 22A). At this time, the transition detector 25sets both the pre-emphasis control signals MUP and MDN to “0”(inactive), as illustrated in FIG. 5. Accordingly, as illustrated inFIG. 22A, the signal SIGA changes from the high-level voltage VH to thelow-level voltage VL, the signal SIGB changes from the low-level voltageVL to the high-level voltage VH, and the signal SIGC maintains themedium-level voltage VM. In other words, in a case where the symboltransits from “+x” to “−x”, none of transitions of the differences AB,BC, and CA corresponds to the transitions W21 and W22; therefore, thepre-emphasis controllers 68A, 68B, and 68C controls the driver units69A, 69B, and 69C not to perform the pre-emphasis operation.

Moreover, in a case where the symbol DS is “+x” and the transitionsignals TxF9, TxR9, and TxP9 are “010”, the symbol transits from “+x” to“+y” (FIG. 22B). At this time, as illustrated in FIG. 5, the transitiondetector 25 sets the pre-emphasis control signal MDN to “1” (active),and sets the pre-emphasis control signal MUP to “0” (inactive).Accordingly, as illustrated in FIG. 22B, the signal SIGA changes fromthe high-level voltage VH to the medium-level voltage VM through themedium-level voltage VMminus, the signal SIGB changes from the low-levelvoltage VL to the high-level voltage VH, and the signal SIGC changesfrom the medium-level voltage VM to the low-level voltage VL through thelow-level voltage VLplus. At this time, the pre-emphasis controller 68Acontrols the driver unit 69A to set the voltage of the signal SIGA tothe medium-level voltage VMnius that is slightly lower than themedium-level voltage VM in a first half time period (0.5 UI) of a timeperiod in which the transmission device 50 outputs the symbol “+y”.Likewise, the pre-emphasis controller 68C controls the driver unit 69Cto set the voltage of the signal SIGC to the low-level voltage VLplusthat is slightly higher than the low-level voltage VL in the first halftime period (0.5 UI) of the time period in which the transmission device50 outputs the symbol “+y”. In other words, the transition of thedifference AB corresponds to the transition W22, and has a possibilitythat the transition time of the difference AB becomes long; therefore,the pre-emphasis controllers 68A and 68C control the driver units 69Aand 69C to perform the pre-emphasis operation.

Further, in a case where the symbol DS is “+x” and the transitionsignals TxF9, TxR9, and TxP9 are “011”, the symbol transits from “+x” to“−y” (FIG. 22C).

At this time, the transition detector 25 sets both the pre-emphasiscontrol signals MUP and MDN to “0” (inactive), as illustrated in FIG. 5.Accordingly, as illustrated in FIG. 22C, the signal SIGA changes fromthe high-level voltage VH to the medium-level voltage VM, the signalSIGB maintains the low-level voltage VL, and the signal SIGC changesfrom the medium-level voltage VM to the high-level voltage VH. In otherwords, in a case where the symbol transits from “+x” to “−y”, none ofthe transitions of the differences AB, BC, and CA corresponds to thetransitions W21 and W22; therefore, the pre-emphasis controllers 68A,68B, and 68C controls the driver units 69A, 69B, and 69C not to performthe pre-emphasis operation.

Furthermore, in a case where the symbol DS is “+x” and the transitionsignals TxF9, TxR9, and TxP9 are “000”, the symbol transits from “+x” to“+z” (FIG. 22D). At this time, the transition detector 25 sets thepre-emphasis control signal MUP to “1” (active), and sets thepre-emphasis control signal MDN to “0” (inactive), as illustrated inFIG. 5. Accordingly, as illustrated in FIG. 22D, the signal SIGA changesfrom the high-level voltage VH to the low-level voltage VL, the signalSIGB changes from the low-level voltage VL to the medium-level voltageVM through the medium-level voltage VMplus, and the signal SIGC changesfrom the medium-level voltage VM to the high-level voltage VH throughthe high-level voltage VHminus. At this time, the pre-emphasiscontroller 68B controls the driver unit 69B to set the voltage of thesignal SIGB to the medium-level voltage VMplus that is slightly higherthan the medium-level voltage VM in a first half time period (0.5 UI) ofa time period in which the transmission device 10 outputs the symbol“+z”. Likewise, the pre-emphasis controller 68C controls the driver unit69B to set the voltage of the signal SIGC to the high-level voltageHMminus that is slightly lower than the high-level voltage VH in thefirst half time period (0.5 UI) of the time period in which thetransmission device 10 outputs the symbol “+z”. In other words, thetransition of the difference AB corresponds to the transition W22, andhas a possibility that the transition time of the difference AB becomeslong; therefore, the pre-emphasis controllers 68B and 68C controls thedriver units 69B and 69C to perform the pre-emphasis operation.

Moreover, in a case where the symbol DS is “+x” and the transitionsignals TxF9, TxR9, and TxP9 are “001”, the symbol transits from “+x” to“−z” (FIG. 22E). At this time, the transition detector 25 sets both thepre-emphasis control signals MUP and MDN to “0” (inactive), asillustrated in FIG. 5. Accordingly, as illustrated in FIG. 22E, thesignal SIGA maintains the high-level voltage VH, the signal SIGB changesfrom the low-level voltage VL to the medium-level voltage VM, and thesignal SIGC changes from the medium-level voltage VM to the low-levelvoltage VL. In other words, in a case where the symbol transits from“+x” to “−z”, none of the transitions of the differences AB, BC, and CAcorresponds to the transitions W21 and W22, therefore, the pre-emphasiscontrollers 68A, 68B, and 68C control the driver units 69A, 69B, and 69Cnot to perform the pre-emphasis operation.

As described above, in the communication system 2, not only the driverunit that outputs the medium-level voltage VM after the transition, butalso the driver unit that outputs the high-level voltage VH or low-levelvoltage VL performs the pre-emphasis operation. Accordingly, in thecommunication system 2, pre-emphasis works strongly, which makes itpossible to enhance waveform quality, for example, in a case where thetransmission path 100 is longer, as compared with the communicationsystem 1.

FIG. 23 illustrates eye diagrams of the difference AB between the signalSIGA and the signal SIGB, the difference BC between the signal SIGB andthe signal SIGC, and the difference CA between the signal SIGC and thesignal SIGA. In the communication system 2 (FIG. 23) according to thepresent embodiment, pre-emphasis works strongly, which makes it possibleto widen an eye opening more than a case of the communication system 1according to the first embodiment (FIGS. 14B to 14C). As a result, it ispossible to enhance communication performance in the communicationsystem 2.

Moreover, in the communication system 2, in a case where one driver unitof the driver units 69A, 69B, and 69C outputs the medium-level voltageVMminus that is lower than the medium-level voltage VM, another driverunit outputs the low-level voltage VLplus that is higher than thelow-level voltage VL, as illustrated in FIG. 22B. Further, in a casewhere one driver unit of the driver units 69A, 69B, and 69C outputs themedium-level voltage VMplus that is higher than medium-level voltage VM,another driver unit outputs the high-level voltage VHminus that is lowerthan the high-level voltage VH, as illustrated in FIG. 22D. This makesit possible to suppress variations in a common mode voltage that is anaverage voltage of the three signals SIGA, SIGB, and SIGC in thecommunication system 2. As a result, in the communication system 2, itis possible to reduce a possibility that electro-magnetic interference(EMI) occurs, which makes it possible to enhance communicationperformance.

As described above, in the present embodiment, not only the driver unitthat outputs the medium-level voltage VM after the transition, but alsothe driver unit that outputs the high-level voltage VH or the low-levelvoltage VL performs the pre-emphasis operation, which makes it possibleto enhance communication performance.

In the present embodiment, in a case where one driver unit outputs themedium-level voltage VMminus, another driver unit outputs the low-levelvoltage VLplus, and in a case where one driver unit outputs themedium-level voltage VMplus, another driver unit outputs the high-levelvoltage VHminus, which makes it possible to suppress variations incommon mode voltage. As a result, it is possible to reduce thepossibility that electro-magnetic interference occurs, which makes itpossible to enhance communication performance.

<3. Application Examples>

Next, description is given of application examples of the communicationsystems described in the foregoing embodiments and modificationexamples.

Application Example 1

FIG. 24 illustrates an external appearance of a smartphone 300 (amulti-functional mobile phone) to which the communication systemaccording to any of the foregoing embodiments, etc. is applied. Variousdevices are mounted in the smartphone 300. The communication systemaccording to any of the foregoing embodiments, etc. is applied to acommunication system that exchanges data between these devices.

FIG. 25 illustrates a configuration example of an application processor310 used in the smartphone 300. The application processor 310 includes aCPU (Central Processing Unit) 311, a memory controller 312, a powersource controller 313, an external interface 314, a GPU (GraphicsProcessing Unit) 315, a media processor 316, a display controller 317,and a MIPI (Mobile industry Processor interface) interface 318. In thisexample, the CPU 311, the memory controller 312, the power sourcecontroller 313, the external interface 314, the GPU 315, the mediaprocessor 316, and the display controller 317 are coupled to a systembus 319 to allow for mutual data exchange through the system bus 319.

The CPU 311 processes various pieces of information handled in thesmartphone 300 in accordance with a program. The memory controller 312controls the memory 501 used in a case where the CPU 311 performsinformation processing. The power source controller 313 controls a powersource of the smartphone 300.

The external interface 314 is an interface for communication withexternal devices. In this example, the external interface 314 is coupledto a wireless communication unit 502 and an image sensor 410. Thewireless communication unit 502 carries out wireless communication withmobile phone base stations. The wireless communication unit 502includes, for example, a baseband unit, an RF (radio frequency) frontend unit, etc. The image sensor 410 acquires an image, and includes, forexample, a CMOS sensor.

The GPU 315 performs image processing. The media processor 316 processesinformation such as voice, characters, and graphics. The displaycontroller 317 controls the display 504 through the MIPI interface 318.The MIPI interface 318 transmits an image signal to the display 504. Asthe image signal, it is possible to use, for example, a YUV-formatsignal, an RGB-format signal, etc. The MIPI interface 318 operates onthe basis of a reference clock supplied from an oscillator circuit 330including a crystal resonator. For example, the communication systemaccording to any of the foregoing embodiments, etc. is applied to acommunication system between the MIPI interface 318 and the display 504.

FIG. 26 illustrates a configuration example of the image sensor 410. Theimage sensor 410 includes a sensor 411, an TSP (Image Signal Processor)412, a MEG (Joint Photographic Experts Group) encoder 413, a CPU 414, aRAM (Random Access Memory) 415, a ROM (Read Only Memory) 416, a powersource controller 417, an I²C (inter-integrated circuit) interface 418,and an MIPI interface 419. In this example, these respective blocks arecoupled to a system bus 420 to allow for mutual data exchange throughthe system bus 420.

The sensor 411 acquires an image, and includes, for example, a CMOSsensor. The ISP 412 performs predetermined processing on the imageacquired by the sensor 411. The JPEG encoder 413 encodes the imageprocessed by the ISP 412 to generate a JPEG-format image. The CPU 414controls respective blocks of the image sensor 410 in accordance with aprogram. The RAM 415 is a memory used in a case where the CPU 414performs information processing. The ROM 416 stores a program to beexecuted in the CPU 414, a setting value obtained by calibration, etc.The power source controller 417 controls a power source of the imagesensor 410. The I²C interface 418 receives a control signal from theapplication processor 310. Although not illustrated, the image sensor410 also receives a clock signal from the application processor 310, inaddition to the control signal. Specifically, the image sensor 410 isoperable on the basis of clock signals of various frequencies. The MIPIinterface 419 transmits an image signal to the application processor310. As the image signal, it is possible to use, for example, aYUV-format signal, an RGB-format signal, etc. The MIPI interface 419operates on the basis of a reference clock supplied from an oscillatorcircuit 430 including a crystal resonator, for example. For example, thecommunication system according to any of the foregoing embodiments, etc.is applied to a communication system between the MIPI interface 419 andthe application processor 310.

Application Example 2

FIG. 27 illustrates a configuration example of a vehicle control system600 to which the communication system according to any of the foregoingembodiments, etc. is applied. The vehicle control system 600 controls anoperation of an automobile, an electric vehicle, a hybrid electricvehicle, a motorcycle, or the like. The vehicle control system 600includes a driving system control unit 610, a body system control unit620, a battery control unit 630, an outside-vehicle informationdetection unit 640, an in-vehicle information detection unit 650, and anintegrated control unit 660. These units are coupled to one anotherthrough a communication network 690. The communication network 690 isallowed to use, for example, a network compliant with any of standardssuch as CAN (Controller Area Network), LIN (Local Interconnect Network),LAN (Local Area Network), and FlexRay (registered trademark). Each ofthe units includes, for example, a microcomputer, a storage section, adrive circuit that drives a device to be controlled, a communicationI/F, and the like.

The driving system control unit 610 controls an operation of a devicerelated to a driving system of a vehicle. The driving system controlunit 610 is coupled to a vehicle state detector 611. The vehicle statedetector 611 detects a state of the vehicle, and includes, for example,a gyro sensor, an acceleration sensor, sensors that detect an operationamount of an accelerator pedal, an operation amount of a brake pedal, asteering angle, etc, and the like. The driving system control unit 610controls the operation of the device related to the driving system ofthe vehicle on the basis of information detected by the vehicle statedetector 611. The communication system according to any of the foregoingembodiments, etc. is applied to a communication system between thedriving system control unit 610 and the vehicle state detector 611.

The body system control unit 620 controls operations of various kinds ofdevices, such as a keyless entry system, a power window device, variouskinds of lamps, mounted in the vehicle.

The battery control unit 630 controls a battery 631. The battery controlunit 630 is coupled to the battery 631. The battery 631 supplieselectric power to a driving motor, and includes, for example, asecondary battery, a cooling device, and the like. The battery controlunit 630 obtains information such as a temperature, an output voltage,and an amount of remaining battery charge from the battery 631, andcontrols the cooling device, etc. of the battery 631 on the basis of theinformation. The communication system according to any of the foregoingembodiments, etc. is applied to a communication system between thebattery control unit 630 and the battery 631.

The outside-vehicle information detection unit 640 detectsoutside-vehicle information. The outside-vehicle information detectionunit 640 is coupled to an imaging section 641 and an outside-vehicleinformation detector 642. The imaging section 641 takes an image outsidethe vehicle, and includes, for example, a ToF (Time Of Flight) camera, astereo camera, a monocular camera, an infrared camera, and the like. Theoutside-vehicle information detector 642 detects outside-vehicleinformation, and includes, for example, a sensor that detectsatmospheric conditions or weather conditions, a sensor that detectsanother vehicle, an obstacle, a pedestrian, etc. around the vehicle, andthe like. The outside-vehicle information detection unit 640 recognizes,for example, the atmospheric conditions, the weather conditions, roadsurface conditions, etc, on the basis of the image taken by the imagingsection 641 and the information detected by the outside-vehicleinformation detector 642, and detects an object such as another vehicle,an obstacle, a pedestrian, and a sign around the vehicle, and acharacter on a road surface, or detects a distance between the objectand the vehicle. The communication system according to any or theforegoing embodiments, etc. is applied to a communication system betweenthe outside-vehicle information detection it 640 and each of the imagingsection 641 and the outside-vehicle information detector 642.

The in-vehicle information detection unit 650 detects in-vehicleinformation. The in-vehicle information detection unit 650 is coupled toa driver state detector 651. The driver state detector 651 detects astate of a driver, and includes, for example, a camera, a biosensor, amicrophone, and the like. The in-vehicle information detection unit 650monitors a degree of fatigue of the driver, a degree of concentration ofthe driver, whether the driver is dozing, etc. on the basis ofinformation detected by the driver state detector 651. The communicationsystem according to any of the foregoing embodiments etc. is applied toa communication system between the in-vehicle information detection unit650 and the driver state detector 651.

The integrated control unit 660 controls an operation of the vehiclecontrol system 600. The integrated control unit 660 is coupled to anoperation section 661, a display section 662, and an instrument panel663. The operation section 661 is operated by an occupant, and includes,for example, a touch panel, various kinds of buttons and switches, andthe like. The display section 662 displays an image, and is configuredwith use of, for example, a liquid crystal display panel. The instrumentpanel 663 displays a state of the vehicle, and includes meters such as aspeed meter, various kinds of alarm lamps, and the like. Thecommunication system according to any of the foregoing embodiments, etc.is applied to a communication system between the integrated control unit660 and each of the operation section 661, the display section 662, andthe instrument panel 663.

Although the present technology has been described above with referenceto some embodiments, modification examples, and application examples toelectronic apparatuses, the present technology is not limited thereto,and may be modified in a variety of ways.

For example, in the foregoing respective embodiments, in the case wherethe transition signals TxF9, TxR9, RxP9 are “000” or “010”, thepre-emphasis operation is performed; however, the foregoing embodiments,etc. are not limited thereto, and the pre-emphasis operation may beperformed in any other cases.

It is to be noted that the effects described in the presentspecification are illustrative and non-limiting, and other effects maybe included.

It is to be noted that the present technology may have the followingconfigurations.

(1)

A transmission device, including:

a driver unit that transmits a data signal with use of a first voltagestate, a second voltage state, and a third voltage state interposedbetween the first voltage state and the second voltage state, and isconfigured to make a voltage in the third voltage state changeable; and

a controller that changes the voltage in the third voltage state tocause the driver unit to perform emphasis.

(2)

The transmission device according to (1), in which the controllerdetermines whether or not to cause the driver unit to perform emphasisin accordance with change among the first voltage state, the secondvoltage state, and the third voltage state.

(3)

The transmission device according to (2), in which

the data signal indicates a sequence of symbols, and

the controller determines whether or not to cause the driver unit toperform emphasis on the basis of a predetermined symbol transition inthe sequence.

(4)

The transmission device according to (3), in which

the driver unit includes:

a first driver unit that selectively sets a voltage state at a firstoutput terminal to one of the first voltage state, the second voltagestate, and the third voltage state,

a second driver unit that selectively sets a voltage state at a secondoutput terminal to one of the first voltage state, the second voltagestate, and the third voltage state, and

a third driver unit that selectively sets a voltage state at a thirdoutput terminal to one of the first voltage state, the second voltagestate, and the third voltage state, and

the voltage states at the first output terminal, the second outputterminal, and the third output terminal are different from one another.

(5)

The transmission device according to (4), further including a signalgenerator that generates a symbol signal on the basis of a transitionsignal indicating the transition of the symbol, in which

the first driver unit, the second driver unit, and the third driver unitrespectively set the voltage states at the first output terminal, thesecond output terminal, and the third output terminal on the basis ofthe symbol signal, and

the controller detects the predetermined symbol transition on the basisof the transition signal to determine whether or not to cause the driverunit to perform emphasis.

(6)

The transmission device according to (5), in which the controllerchanges the voltage in the third voltage state upon a symbol transitionthat causes the voltage state at the first output terminal, the voltagestate at the second output terminal, and the voltage state at the thirdoutput terminal to change together, thereby causing the emphasis to beperformed.

(7)

The transmission device according to (6), in which the controller alsochanges the voltage in the first voltage state or the voltage in thesecond voltage sate upon the symbol transition that causes the voltagestate at the first output terminal, the voltage state at the secondoutput terminal, and the voltage state at the third output terminal tochange together, thereby causing the emphasis to be performed.

(8)

The transmission device according to any one of (4) to (7), in which

the first driver unit includes:

a first circuit provided in a path from a first power source to thefirst output terminal, and

a second circuit provided in a path from a second power source to thefirst output terminal, and

the first driver unit causes a current to pass from the first powersource to the second power source through the first circuit and thesecond circuit, thereby setting the voltage state at the first outputterminal to the third voltage state.

(9)

The transmission device according to (8), in which the controllerchanges an impedance ratio between an impedance in the first circuit andan impedance in the second circuit to change the voltage in the thirdvoltage state.

(10)

The transmission device according to (9), in which the controllerchanges the impedance ratio to cause a parallel impedance of theimpedance in the first circuit and the impedance in the second circuitto be constant.

(11)

The transmission device according to any one of (8) to (10), in which

the first circuit includes a plurality of first sub-circuits eachincluding a first resistor and a first transistor provided in the pathfrom the first power source to the first output terminal,

the second circuit includes a plurality of second sub-circuits eachincluding a second resistor and a second transistor provided in the pathfrom the second power source to the first output terminal, and

the first transistor in one or more of the plurality of firstsub-circuits is turned on and the second transistor in one or more ofthe plurality of second sub-circuits is turned on to set the voltagestate at the first output terminal to the third voltage state.

(12)

The transmission device according to (11), in which the controllerincreases number of first transistors to be turned on of a plurality offirst transistors in the first circuit and decreases number of secondtransistors to be turned on of a plurality of second transistors in thesecond circuit to change the voltage in the third voltage state.

(13)

The transmission device according to (11) or (12), in which

the plurality of first sub-circuits are divided into a plurality offirst groups,

the plurality of second sub-circuits are divided into a plurality ofsecond groups, and

the controller turns on or off a plurality of first transistors in thefirst circuit in a unit of the first group and turns on or off aplurality of second transistors in the second circuit in a unit of thesecond group.

(14)

The transmission device according to (13), in which

the plurality of first groups includes a first sub-group and a secondsub-group, and

the first sub-circuits belonging to the first sub-group are different innumber from the second sub-circuits belonging to the second sub-group.

(15)

The transmission device according to (4), in which

the first driver unit includes:

a first circuit provided in a path from a first power source to thefirst output terminal,

a second circuit provided in a path from a second power source to thefirst output terminal, and

a third circuit that includes a voltage generator and a switch, andturns the switch on to supply the voltage in the third voltage state tothe first output terminal, the voltage generator generating the voltagein the third voltage state.

(16)

A transmission method, including:

transmitting a data signal with use of a first voltage state, a secondvoltage state, and a third voltage state interposed between the firstvoltage state and the second voltage state, and

changing a voltage in the third voltage state to perform emphasis.

(17)

A communication system provided with a transmission device and areception device, the transmission device including:

a driver unit that transmits a data signal with use of a first voltagestate, a second voltage state, and a third voltage state interposedbetween the first voltage state and the second voltage state, and isconfigured to make a voltage in the third voltage state changeable; and

a controller that changes the voltage in the third voltage state tocause the driver unit to perform emphasis.

This application claims the benefit of Japanese Priority PatentApplication No. 2016-017962 filed with the Japan Patent Office on Feb.2, 2016, the entire contents of which are incorporated herein byreference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

The invention claimed is:
 1. A transmission device, comprising: a driverunit that transmits a data signal with use of a first voltage state, asecond voltage state, and a third voltage state interposed between thefirst voltage state and the second voltage state, and is configured tomake a voltage in the third voltage state changeable; and a controllerthat changes the voltage in the third voltage state to cause the driverunit to perform emphasis, wherein the controller determines whether ornot to cause the driver unit to perform emphasis in accordance withchange among the first voltage state, the second voltage state, and thethird voltage state, the data signal indicates a sequence of symbols,the controller changes the voltage in the third voltage state on a basisof a transition of the symbols in the sequence, the driver unitincludes: a first driver unit that selectively sets a voltage state at afirst output terminal to one of the first voltage state, the secondvoltage state, and the third voltage state, a second driver unit thatselectively sets a voltage state at a second output terminal to one ofthe first voltage state, the second voltage state, and the third voltagestate, and a third driver unit that selectively sets a voltage state ata third output terminal to one of the first voltage state, the secondvoltage state, and the third voltage state, and the voltage states thefirst output terminal, the second output terminal, and the third outputterminal are different from one another.
 2. The transmission deviceaccording to claim 1, further comprising a signal generator thatgenerates a symbol signal on a basis of a transition signal indicatingthe transition of the symbol, wherein the first driver unit, the seconddriver unit, and the third driver unit respectively set the voltagestates at the first output terminal, the second output terminal, and thethird output terminal on a basis of the symbol signal, and thecontroller detects the transition of the symbol on a basis of thetransition signal to change the voltage in the third voltage state. 3.The transmission device according to claim 2, wherein the controllerchanges the voltage in the third voltage state upon a symbol transitionthat causes the voltage state at the first output terminal, the voltagestate at the second output terminal, and the voltage state at the thirdoutput terminal to change together, thereby causing the emphasis to beperformed.
 4. The transmission device according to claim 3, wherein thecontroller also changes the voltage in the first voltage state or thevoltage in the second voltage sate upon the symbol transition thatcauses the voltage state at the first output terminal, the voltage stateat the second output terminal, and the voltage state at the third outputterminal to change together, thereby causing the emphasis to beperformed.
 5. The transmission device according to claim 1, wherein thefirst driver unit includes: a first circuit provided in a path from afirst power source to the first output terminal, and a second circuitprovided in a path from a second power source to the first outputterminal, and the first driver unit causes a current to pass from thefirst power source to the second power source through the first circuitand the second circuit, thereby setting the voltage state at the firstoutput terminal to the third voltage state.
 6. The transmission deviceaccording to claim 5, wherein the controller changes an impedance ratiobetween an impedance in the first circuit and an impedance in the secondcircuit to change the voltage in the third voltage state.
 7. Thetransmission device according to claim 6, wherein the controller changesthe impedance ratio to cause a parallel impedance of the impedance inthe first circuit and the impedance in the second circuit to beconstant.
 8. The transmission device according to claim 5, wherein thefirst circuit includes a plurality of first sub-circuits each includinga first resistor and a first transistor provided in the path from thefirst power source to the first output terminal, the second circuitincludes a plurality of second sub-circuits each including a secondresistor and a second transistor provided in the path from the secondpower source to the first output terminal, and the first transistor inone or more of the plurality of first sub-circuits is turned on and thesecond transistor in one or more of the plurality of second sub-circuitsis turned on to set the voltage state at the first output terminal tothe third voltage state.
 9. The transmission device according to claim8, wherein the controller increases number of first transistors to beturned on of a plurality of first transistors in the first circuit anddecreases number of second transistors to be turned on of a plurality ofsecond transistors in the second circuit to change the voltage in thethird voltage state.
 10. The transmission device according to claim 8,wherein the plurality of first sub-circuits are divided into a pluralityof first groups, the plurality of second sub-circuits are divided into aplurality of second groups, and the controller turns on or off aplurality of first transistors in the first circuit in a unit of thefirst group and turns on or off a plurality of second transistors in thesecond circuit in a unit of the second group.
 11. The transmissiondevice according to claim 10, wherein the plurality of first groupsincludes a first sub-group and a second sub-group, and the firstsub-circuits belonging to the first sub-group are different in numberfrom the second sub-circuits belonging to the second sub-group.
 12. Thetransmission device according to claim 1, wherein the first driver unitincludes: a first circuit provided in a path from a first power sourceto the first output terminal, a second circuit provided in a path from asecond power source to the first output terminal, and a third circuitthat includes a voltage generator and a switch, and turns the switch onto supply the voltage in the third voltage state to the first outputterminal, the voltage generator generating the voltage in the thirdvoltage state.
 13. The transmission device according to claim 1, whereinthe controller selectively changes a voltage in the first voltage stateor the second voltage state in addition to the third voltage state tocause the driver unit to perform emphasis.
 14. The transmission deviceaccording to claim 1, wherein the controller changes the voltage in thethird voltage state while controlling an output impedance of the driverunit to be constant.
 15. A transmission device, comprising: a driverunit that transmits a data signal with use of a first voltage state, asecond voltage state, and a third voltage state interposed between thefirst voltage state and the second voltage state, and is configured tomake a voltage in the third voltage state changeable; and a controllerthat changes the voltage in the third voltage state to cause the driverunit to perform emphasis, wherein the driver unit includes: a firstdriver unit that selectively sets a voltage state at a first outputterminal to one of the first voltage state, the second voltage state,and the third voltage state, a second driver unit that selectively setsa voltage state at a second output terminal to one of the first voltagestate, the second voltage state, and the third voltage state, and athird driver unit that selectively sets a voltage state at a thirdoutput terminal to one of the first voltage state, the second voltagestate, and the third voltage state, the voltage states at the firstoutput terminal, the second output terminal, and the third outputterminal are different from one another, the controller changes avoltage in the first voltage state while controlling an output impedanceof the first driver unit to be constant, the controller changes avoltage in the second voltage state while controlling an outputimpedance of the second driver unit to be constant, and the controllerchanges the voltage in the third voltage state while controlling anoutput impedance of the third driver unit to be constant.
 16. Acommunication system provided with a transmission device and a receptiondevice, the transmission device comprising: a driver unit that transmitsa data signal with use of a first voltage state, a second voltage state,and a third voltage state interposed between the first voltage state andthe second voltage state, and is configured to make a voltage in thethird voltage state changeable; and a controller that changes thevoltage in the third voltage state to cause the driver unit to performemphasis, wherein the controller determines whether or not to cause thedriver unit to perform emphasis in accordance with change among thefirst voltage state, the second voltage state, and the third voltagestate, the data signal indicates a sequence of symbols, the controllerchanges the voltage in the third voltage state on a basis of atransition of the symbols in the sequence, the driver unit includes: afirst driver unit that selectively sets a voltage state at a firstoutput terminal to one of the first voltage state, the second voltagestate, and the third voltage state, a second driver unit thatselectively sets a voltage state at a second output terminal to one ofthe first voltage state, the second voltage state, and the third voltagestate, and a third driver unit that selectively sets a voltage state ata third output terminal to one of the first voltage state, the secondvoltage state, and the third voltage state, and the voltage states thefirst output terminal, the second output terminal, and the third outputterminal are different from one another.